Antioxidants for female subfertility

Marian G Showell; Rebecca Mackenzie-Proctor; Vanessa Jordan; Roger J Hart

doi:10.1002/14651858.CD007807.pub4

. 2020 Aug 27;2020(8):CD007807. doi: 10.1002/14651858.CD007807.pub4

Antioxidants for female subfertility

Marian G Showell ^1,^✉, Rebecca Mackenzie-Proctor ², Vanessa Jordan ¹, Roger J Hart ³

Editor: Cochrane Gynaecology and Fertility Group

PMCID: PMC8094745 PMID: 32851663

Abstract

Background

A couple may be considered to have fertility problems if they have been trying to conceive for over a year with no success. This may affect up to a quarter of all couples planning a child. It is estimated that for 40% to 50% of couples, subfertility may result from factors affecting women. Antioxidants are thought to reduce the oxidative stress brought on by these conditions. Currently, limited evidence suggests that antioxidants improve fertility, and trials have explored this area with varied results. This review assesses the evidence for the effectiveness of different antioxidants in female subfertility.

Objectives

To determine whether supplementary oral antioxidants compared with placebo, no treatment/standard treatment or another antioxidant improve fertility outcomes for subfertile women.

Search methods

We searched the following databases (from their inception to September 2019), with no language or date restriction: Cochrane Gynaecology and Fertility Group (CGFG) specialised register, CENTRAL, MEDLINE, Embase, PsycINFO, CINAHL and AMED. We checked reference lists of relevant studies and searched the trial registers.

Selection criteria

We included randomised controlled trials (RCTs) that compared any type, dose or combination of oral antioxidant supplement with placebo, no treatment or treatment with another antioxidant, among women attending a reproductive clinic. We excluded trials comparing antioxidants with fertility drugs alone and trials that only included fertile women attending a fertility clinic because of male partner infertility.

Data collection and analysis

We used standard methodological procedures expected by Cochrane. The primary review outcome was live birth; secondary outcomes included clinical pregnancy rates and adverse events.

Main results

We included 63 trials involving 7760 women. Investigators compared oral antioxidants, including: combinations of antioxidants, N‐acetylcysteine, melatonin, L‐arginine, myo‐inositol, carnitine, selenium, vitamin E, vitamin B complex, vitamin C, vitamin D+calcium, CoQ10, and omega‐3‐polyunsaturated fatty acids versus placebo, no treatment/standard treatment or another antioxidant. Only 27 of the 63 included trials reported funding sources.

Due to the very low‐quality of the evidence we are uncertain whether antioxidants improve live birth rate compared with placebo or no treatment/standard treatment (odds ratio (OR) 1.81, 95% confidence interval (CI) 1.36 to 2.43; P < 0.001, I² = 29%; 13 RCTs, 1227 women). This suggests that among subfertile women with an expected live birth rate of 19%, the rate among women using antioxidants would be between 24% and 36%.

Low‐quality evidence suggests that antioxidants may improve clinical pregnancy rate compared with placebo or no treatment/standard treatment (OR 1.65, 95% CI 1.43 to 1.89; P < 0.001, I² = 63%; 35 RCTs, 5165 women). This suggests that among subfertile women with an expected clinical pregnancy rate of 19%, the rate among women using antioxidants would be between 25% and 30%. Heterogeneity was moderately high.

Overall 28 trials reported on various adverse events in the meta‐analysis. The evidence suggests that the use of antioxidants makes no difference between the groups in rates of miscarriage (OR 1.13, 95% CI 0.82 to 1.55; P = 0.46, I² = 0%; 24 RCTs, 3229 women; low‐quality evidence). There was also no evidence of a difference between the groups in rates of multiple pregnancy (OR 1.00, 95% CI 0.63 to 1.56; P = 0.99, I² = 0%; 9 RCTs, 1886 women; low‐quality evidence). There was also no evidence of a difference between the groups in rates of gastrointestinal disturbances (OR 1.55, 95% CI 0.47 to 5.10; P = 0.47, I² = 0%; 3 RCTs, 343 women; low‐quality evidence). Low‐quality evidence showed that there was also no difference between the groups in rates of ectopic pregnancy (OR 1.40, 95% CI 0.27 to 7.20; P = 0.69, I² = 0%; 4 RCTs, 404 women).

In the antioxidant versus antioxidant comparison, low‐quality evidence shows no difference in a lower dose of melatonin being associated with an increased live‐birth rate compared with higher‐dose melatonin (OR 0.94, 95% CI 0.41 to 2.15; P = 0.89, I² = 0%; 2 RCTs, 140 women). This suggests that among subfertile women with an expected live‐birth rate of 24%, the rate among women using a lower dose of melatonin compared to a higher dose would be between 12% and 40%. Similarly with clinical pregnancy, there was no evidence of a difference between the groups in rates between a lower and a higher dose of melatonin (OR 0.94, 95% CI 0.41 to 2.15; P = 0.89, I² = 0%; 2 RCTs, 140 women).

Three trials reported on miscarriage in the antioxidant versus antioxidant comparison (two used doses of melatonin and one compared N‐acetylcysteine versus L‐carnitine). There were no miscarriages in either melatonin trial. Multiple pregnancy and gastrointestinal disturbances were not reported, and ectopic pregnancy was reported by only one trial, with no events. The study comparing N‐acetylcysteine with L‐carnitine did not report live birth rate. Very low‐quality evidence shows no evidence of a difference in clinical pregnancy (OR 0.81, 95% CI 0.33 to 2.00; 1 RCT, 164 women; low‐quality evidence). Low quality evidence shows no difference in miscarriage (OR 1.54, 95% CI 0.42 to 5.67; 1 RCT, 164 women; low‐quality evidence). The study did not report multiple pregnancy, gastrointestinal disturbances or ectopic pregnancy.

The overall quality of evidence was limited by serious risk of bias associated with poor reporting of methods, imprecision and inconsistency.

Authors' conclusions

In this review, there was low‐ to very low‐quality evidence to show that taking an antioxidant may benefit subfertile women. Overall, there is no evidence of increased risk of miscarriage, multiple births, gastrointestinal effects or ectopic pregnancies, but evidence was of very low quality. At this time, there is limited evidence in support of supplemental oral antioxidants for subfertile women.

Plain language summary

Vitamins and minerals for subfertility in women

Review question: Do supplementary oral antioxidants compared with placebo, with no treatment/standard treatment or with another antioxidant improve fertility outcomes for subfertile women? 'Standard treatment' includes less than 1 mg of folic acid.

Background: Many subfertile women undergoing fertility treatment also take dietary supplements in the hope of improving their fertility. This can be a very stressful time for women and their partners. It is important that these couples are given high‐quality evidence that will allow them to make informed decisions on whether taking a supplemental antioxidant when undergoing fertility treatment will improve their chances or cause any adverse effects. This is especially important, as most antioxidant supplements are uncontrolled by regulation. This review aimed to assess whether supplements with oral antioxidants increase a subfertile woman's chances of becoming pregnant and having a baby.

Search date: The evidence is current to September 2019.

Study characteristics: The review includes 63 randomised controlled trials that compare antioxidants with placebo or with no treatment/standard treatment, or with another antioxidant, in a total of 7760 women.

Funding sources: Funding sources were reported by only 27 of the 63 included trials.

Key results: We are uncertain whether the use of antioxidants will increase live births, as the evidence was of very low quality. Based on our results, we would expect that out of 100 subfertile women not taking antioxidants, 20 would have a baby, compared with between 24 and 36 women per 100 who would have a baby if taking antioxidants. Low‐quality evidence suggests that antioxidants may be associated with increased clinical pregnancy rates. Adverse effects were poorly reported, but the use of antioxidants did not appear to lead to more miscarriages, multiple births, digestive effects or ectopic pregnancies.

Low‐quality evidence suggests that there is no difference in live birth or clinical pregnancy rates when comparing a lower dose of melatonin to a higher dose. Here we would expect that out of 100 subfertile women taking low‐dose melatonin, 24 would have a baby, compared with between 12 and 40 women per 100 who would have a baby if taking higher‐dose melatonin.

The study comparing N‐acetylcysteine with L‐carnitine did not report live birth rate. Very low‐quality evidence shows no evidence of a difference in clinical pregnancy. Low quality evidence shows no difference in miscarriage. The study did not report multiple pregnancy, gastrointestinal disturbances or ectopic pregnancy.

Quality of the evidence: The overall quality of evidence was limited by serious risks of bias associated with poor reporting of methods, imprecision and inconsistency.

Summary of findings

Background

Description of the condition

A couple that has tried to conceive for a year or longer without success is considered to be subfertile (Practice Committee of ARSM 2020) or less fertile than a typical couple. The World Health Organization (WHO) (Zegers‐Hochschild 2009) defines infertility as the “failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse”. Levels of infertility in 2010 were similar to those in 1990 in most of the world, apart from declines in Sub‐Saharan Africa and in South Asia (Mascarenhas 2012). Thirty to forty per cent of cases of subfertility are due to causes in women (WHO). Influencing factors include ovulatory failure, tubal damage, endometriosis, poor egg quality and unexplained subfertility. It is suggested that up to 25% of couples who are planning a baby have difficulty (Boivin 2007; Hart 2003). Nine per cent of men and 11% of women of reproductive age are thought to experience infertility (Chandra 2013)

To overcome these fertility problems, many couples undergo assisted fertility techniques (assisted reproductive techniques (ART)). These include ovulation stimulation, intrauterine insemination (IUI), in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI).

Women use antioxidant supplements in preparation for ART or simultaneously with the treatment, or both, and some women use supplements alone with no ART in an attempt to improve their fertility.

Description of the intervention

Antioxidants are biological and chemical compounds that reduce oxidative damage, the imbalance between creation of reactive oxygen species and the body's ability to detoxify. They are a group of organic nutrients that include vitamins, minerals and polyunsaturated fatty acids (PUFAs). Some of the predominant antioxidants used in female subfertility are N‐acetylcysteine; melatonin; vitamins A, C and E; folic acid; myo‐inositol; zinc and selenium. They may be administered as a single antioxidant or as combined therapy.

PUFAs are classified into omega‐3, omega‐6 and omega‐9. Omega‐9 is synthesised by animals, but omega‐3 and ‐6 need to be supplemented in the diet. The main sources of omega‐6 are vegetable oils. Sources of omega‐3 are vegetable and fish oils. The ratio of omega‐6 to omega‐3 has risen in recent times (as a result of increased intake of vegetable oils) to the point where there is a reduced need for intake of omega‐6 and an increased need for intake of omega‐3 (Wathes 2007).

The amino acid L‐arginine also has antioxidant properties that aid in the inflammatory response and act against oxidative damage (Ko 2012).

When oxidative damage occurs, toxins are produced as a consequence of all cells using oxygen to survive. Toxic end‐products may include molecules that have unpaired electrons, which may lead to the formation of free radicals. Free radicals may cause further harmful reactions with lipids in membranes, amino acids in proteins and carbohydrates within nucleic acids. An antioxidant molecule is thought to be capable of slowing or preventing the oxidation of other molecules, and potentially of reducing the production of free radicals, which may cause this cellular damage.

Two major types of free radicals have been identified: reactive oxygen species (ROS) and reactive nitrogen species (RNS). Reactive oxygen species are products of normal cellular metabolism and consist of oxygen ions, free radicals and peroxides. The addition of one electron to oxygen forms the superoxide anion radical, which can then be converted to hydroxyl radical, peroxyl radical or hydrogen peroxide. Free radicals seek to participate in chemical reactions that relieve them of their unpaired electron, resulting in oxidation (Ruder 2008; Tremellen 2008). The presence of ROSs within the ovary and the endometrium may have physiological and pathological implications for women when they try to conceive. Oxidative stress (OS) is a result of an imbalance between the amount of ROS and the quantity of natural antioxidants present within the body, and results in overwhelming the body’s natural defence mechanism. ROS can attack lipids, proteins DNA and affect metabolic pathways (chemical transformations in the cells) (Agarwal 2012). Natural antioxidants present in the body include catalase, glutathione peroxidase, superoxide dismutase and glutathione reductase, vitamins C and E, ferritin and transferrin (Gupta 2007).

Indirect evidence from smoking and alcohol trials suggests that these factors have a negative impact on female fertility, potentially through the generation of excessive oxidative stress (Agarwal 2012; Ruder 2008). Other lifestyle factors such as diet, disease, pollution, stress and allergies also contribute to increased levels of free radicals (Agarwal 2012).

The global vitamin and supplement market has grown exponentially and has been reported in 2016 as being worth over USD 140 billion, and projected to reach USD 230 billion by 2027 (Global Supplement Report 2019; Global Supplement report 2016; Reportlinker.com 2010). In the UK there has been a 13.8% growth in vitamin and supplement manufacturing from 2015 to 2020. In 2009 sales of vitamins and dietary supplements in the UK "totalled £674.6 million, a growth of about 16% over the previous five years, with the two biggest‐selling areas being multivitamins (GBP 138.6 million) and fish oils (GBP 139.1 million)" (NHS News 2011). Vitamins and supplements are dispensed through various retail outlets, including health‐food shops, online retailers, health centres, fitness clubs, supermarkets and pharmacies.

In an effort to enhance fertility, couples are increasingly resorting to ART; however, these techniques do not cure the causes of subfertility, but rather overcome some of its barriers. Adjunctive measures, including courses of dietary supplements such as oral antioxidants, may be beneficial (Ebisch 2007). However, most antioxidant supplements are uncontrolled by regulation, and thus their effects may be unpredictable in the population.

How the intervention might work

Antioxidants are said to have an important role in the regulation of all processes involved in the birth of a healthy baby (Gupta 2007). The local development of oxidative stress will have significant adverse effects on these processes. Conditions with which the adverse effects of oxidative stress may be associated in subfertile women include endometriosis, hydrosalpinges (dilated fallopian tubes), polycystic ovary syndrome (PCOS) and potentially unexplained subfertility (Agarwal 2012; Ruder 2008; Zhao 2006).

At the time of conception, oxidative stress can lead to cell membrane lipid peroxidation, cellular protein oxidation and DNA damage, causing a negative effect upon the oocyte (immature egg cell), the embryo and implantation (Ruder 2008). Antioxidants would be expected to counteract the negative impact of oxygen‐free radicals by acting as free radical scavengers.

Supplementary antioxidants may have several methods of action. Fertility benefits of vitamin E include improvement in epithelial growth in blood vessels and in the endometrium (Ledee‐Bataille 2002). Higher vitamin D levels are associated with an increased likelihood of successful pregnancy and may particularly benefit women with PCOS in lowering hyperandrogenism (androgen excess) (Thomson 2012). Myo‐inositol helps ovarian function and decreases hyperandrogenism and insulin resistance (Nestler 1998); L‐arginine improves endometrial blood flow (Takasaki 2009); N‐acetylcysteine is needed for fertile cervical mucus and ovulation (Badawy 2007); and PUFAs influence prostaglandin (lipid compounds with hormone‐like effects) synthesis and steroidogenesis (creation of steroid hormones), and also play a role in the composition of cell membranes of the sperm and oocyte, which is important during fertilisation (Wathes 2007). Cohort studies have shown some evidence suggesting that in some instances taking a multivitamin tablet may increase fertility (Haggarty 2006) or even regulate ovulation (Charvarro 2008).

Why it is important to do this review

There is currently limited evidence on whether antioxidants improve fertility, and ongoing trials in this area show varied results. This review assesses the effectiveness of different antioxidants and different dosages. This is an update of a review first published in 2013 (Showell 2013) and updated in 2017 (Showell 2017).

Subfertile women are highly motivated to explore all avenues of treatment in their desire to have a healthy baby. Antioxidants are mostly unregulated and are readily available for purchase by consumers. Research has suggested that a significant number of women undergoing fertility treatment are taking oral supplements in the expectation that this will improve their chances of conception (O'Reilly 2014; Stankiewicz 2007). Consumer perception is that antioxidant therapy is not associated with harm and is associated only with benefit. It is important to establish whether or not this therapy does improve fertility and whether it is associated with any harm.

Objectives

To determine whether supplementary oral antioxidants compared with placebo, no treatment/standard treatment or another antioxidant improve fertility outcomes for subfertile women.

Methods

Criteria for considering studies for this review

Types of studies

Inclusion criteria

Randomised controlled trials (RCTs).
Cross‐over trials are included, but we used only first‐phase data in the analysis. Achieving outcomes such as pregnancy and live birth would preclude entry of couples into the next trial phase (Dias 2006).

Exclusion criteria

Any quasi‐randomised trials.

Types of participants

Inclusion criteria

Trials that included subfertile women who had been referred to a fertility clinic and might or might not be undergoing assisted reproductive techniques (ART) such as in vitro fertilisation (IVF), intrauterine insemination (IUI) or intracytoplasmic sperm injection (ICSI).

Exclusion criteria

Trials enrolling only fertile women attending a fertility clinic exclusively as the result of male partner infertility.
Trials enrolling women exclusively with any vitamin deficiency.

Types of interventions

Inclusion criteria

Any type of oral antioxidant supplementation versus control: placebo (plus or minus a co‐intervention) or no treatment/standard treatment (standard treatment includes folic acid < 1 mg);
Individual or combined oral antioxidants versus any antioxidant (head‐to‐head trials).

On clinical advice, we analysed trials that used folic acid (standard treatment) and those that included a co‐intervention (a fertility drug such as clomiphene citrate or metformin) in both arms in the antioxidant versus placebo or no treatment/standard treatment comparison, and not in the head‐to‐head comparison, as the controls were not considered to be active treatments.

Exclusion criteria

Interventions that included antioxidants alone versus fertility drugs as controls. These fertility drugs included metformin and clomiphene citrate.

Types of outcome measures

Primary outcomes

Live birth rate per woman randomly assigned: if live birth data were unavailable and the trial reported ongoing pregnancy, we reported ongoing pregnancy as live birth (footnoted in the forest plot). We defined live birth as delivery of a live fetus after 20 completed weeks of gestation, and ongoing pregnancy as evidence of a gestational sac with fetal heart motion at 12 weeks, confirmed with ultrasound.

Secondary outcomes

Clinical pregnancy rate per woman (as confirmed by the identification of a gestational sac on ultrasound at seven or more weeks' gestation).
Any adverse effects reported by the trial. We subgrouped these events by the type of adverse event reported.

Search methods for identification of studies

We searched for all reports, published and unpublished, that described RCTs investigating oral antioxidant supplementation for subfertile women and its impact on live birth, pregnancy and adverse event rates. We used both indexed and free‐text terms, and applied no language or date restrictions.

Electronic searches

We searched the following databases:

The Cochrane Gynaecology and Fertility Group's (CGFG) specialised register of controlled trials; searched 12 September 2019, PROCITE platform (Appendix 1);
CENTRAL, via the Cochrane Register of Studies Online (CRSO); searched 12 September 2019, Web platform (Appendix 2);
MEDLINE; searched from 1946 to 12 September 2019, OVID platform (Appendix 3);
Embase; searched from 1980 to 12 September 2019, OVID platform (Appendix 4);
PsycINFO; searched from 1806 to 12 September 2019, OVID platform (Appendix 5);
AMED (Allied and Complementary Medicine); searched from 1985 to 12 September 2019, OVID platform (Appendix 6);
CINAHL; searched from 1961 to 12 September 2019, EBSCO platform (Appendix 7).

The MEDLINE search was limited by the Cochrane highly sensitive search strategy filter for identifying randomised trials, which appears in the Cochrane Handbook of Systematic Reviews of Interventions (Chapter 6, 6.4.11; Lefebvre 2011). We combined the Embase searches with trial filters developed by the Scottish Intercollegiate Guidelines Network (SIGN) (www.sign.ac.uk/what-we-do/methodology/search-filters/).

Searching other resources

(last searched September 2019):

International trial registers: the ClinicalTrials database, a service of the US National Institutes of Health (clinicaltrials.gov/ct2/home) and the World Health Organization International Trials Registry Platform search portal (www.who.int/trialsearch/Default.aspx);
Web of Knowledge for conference proceedings and published trials;
Google, using the keywords 'antioxidants female infertility' and 'antioxidants female subfertility';
Database for Abstracts of Reviews of Effects (DARE) for other reviews on this topic;
'Grey' literature (unpublished and unindexed), through the openGREY database (www.opengrey.eu/); (Appendix 8).

We also contacted known experts and personal contacts for information on any unpublished materials, and we checked the citation lists of appropriate papers for any relevant references.

Data collection and analysis

We conducted data collection and analysis in accordance with the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2019).

Selection of studies

Two review authors (MGS and RM‐P) independently reviewed titles and abstracts of trials for eligibility. We obtained the full texts of trials that we considered for inclusion. We sought further information from the authors of trials that did not contain sufficient information to make a decision about eligibility. We resolved any disagreements by reference to a third review author. We documented the selection process with a PRISMA flow chart.

Data extraction and management

Two review authors (MGS and RM‐P) independently extracted data from the included trials using a data extraction form. We compared the two sets of extracted data and resolved discrepancies by discussion. The review authors screened the trials to ensure that there were no duplicate publications.

We designed the data extraction forms to extract information on study characteristics and outcomes. We have included this information and present it in the Characteristics of included studies and the Characteristics of excluded studies tables, in keeping with the guidance provided by the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2019). If any information on trial methodology or any trial data were missing, we contacted the study authors by email and by post. The predominant questions for trial authors concerned live birth data, clinical pregnancy, methods of randomisation and allocation concealment.

Assessment of risk of bias in included studies

We assessed the included studies for risks of bias using the Cochrane 'Risk of bias' tool, to assess selection bias (sequence generation and allocation concealment); performance bias (blinding of participants and personnel); detection bias (blinding of outcome assessors); attrition bias (completeness of outcome data); reporting bias (selective outcome reporting); and other potential sources of bias. Two review authors (MGS and RM‐P) assessed the included studies according to these six criteria, resolving any disagreements by discussion with a third review author. We sought published protocols.

We took care to search for within‐study selective reporting, for example trials failing to report outcomes such as live birth or reporting them in insufficient detail to allow inclusion. Where protocols were available, we assessed studies for differences between study protocols and published results.

In cases where included studies failed to identify the primary outcome of live birth but did report pregnancy rates, we carried out an informal assessment to determine whether pregnancy rates were similar to those in studies that reported live birth.

Measures of treatment effect

We expressed the dichotomous data for live birth, pregnancy rate, miscarriage and adverse events as Mantel‐Haenszel odds ratios (ORs) with 95% confidence intervals (95% CIs).

Unit of analysis issues

We analysed the outcomes of live birth, pregnancy and adverse events per woman randomly assigned, counting multiple births as one live birth event.

Dealing with missing data

In cases where trial data were missing, we first sought information from the original trial investigators. Details of authors contacted and the questions asked of them are contained in Characteristics of included studies. In addition, and where possible, we performed analyses on all outcomes on an intention‐to‐treat basis, i.e. to include in the analyses all women randomly assigned to each group and to analyse all women in the group to which they were assigned, regardless of whether or not they received the allocated intervention.

Assessment of heterogeneity

We considered whether the clinical and methodological characteristics of included studies were sufficiently similar for meta‐analysis to provide a clinically meaningful summary. We assessed statistical heterogeneity according to the guidelines set out in the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2019). We examined heterogeneity between the results of different trials by visually examining the forest plots and the overlap of confidence intervals (poor overlap suggested heterogeneity), by considering the P value (a low P value or a large Chi² statistic relative to the degree of freedom suggests heterogeneity), and by identifying the I² statistic. If I² was 50% or higher, we assumed high heterogeneity, and conducted a sensitivity analysis. A high I² statistic suggests that variations in effect estimates were due to differences between trials rather than to chance alone.

Assessment of reporting biases

The search strategies covered multiple sources, without language or publication restrictions. We were alert to the possibility of duplication of data. We used a funnel plot to explore the possibility of small‐study effects in cases where estimates of intervention effect can be more beneficial in smaller studies (Page 2019).

Data synthesis

We conducted statistical analysis of the data using Review Manager 5 (RevMan 2014). We considered pregnancy outcomes to be positive, and higher numbers of pregnancy rates to be a benefit. We considered the outcomes of miscarriage and adverse events to be negative effects, and higher numbers harmful.

We combined data from primary studies using a fixed‐effect model in the following comparisons:

Antioxidants versus control (placebo or no treatment/standard treatment);
Antioxidants versus antioxidants, or head‐to‐head.

We displayed increases in the odds of a particular outcome, which may be beneficial (e.g. live birth) or detrimental (e.g. adverse events), graphically in meta‐analyses to the right of the centre line, and decreases in the odds of a particular outcome to the left of the centre line.

The aim was to define analyses that were comprehensive and mutually exclusive, so that we could slot all eligible study results into one stratum only. We specified comparisons so that any trials falling within each stratum could be pooled for meta‐analysis. Stratification allowed for consideration of effects within each stratum, as well as or instead of an overall estimate for comparison.

In trials with multiple arms, we pooled intervention groups versus the control group.

If individuals had been randomly re‐assigned after failed cycles, we did not pool the data in a meta‐analysis.

Subgroup analysis and investigation of heterogeneity

We conducted the following subgroup analyses:

Type of control, placebo or no treatment;
Type of antioxidant, whether individual or combined (three or more antioxidants combined);
Trials that enrolled women with different indications for infertility (i.e. PCOS, endometriosis, unexplained infertility or poor responders);
Trials that enrolled women who were also undergoing IVF or ICSI.

Sensitivity analysis

We conducted sensitivity analyses on the primary outcomes if we detected a high degree of heterogeneity (where the I² statistic was 50% or more), excluding studies:

with a high risk of bias, or
that used antioxidants plus a fertility drug (a co‐intervention) versus placebo plus a fertility drug

We also conducted a sensitivity analysis on the choice of using a fixed‐effect model by using a random‐effects model.

Overall quality of the body of evidence: 'Summary of findings' tables

We produced a 'Summary of findings' table, using GRADEpro GDT software (GRADEpro GDT 2015) and Cochrane methods (Schünemann 2019) for the main review comparison (Antioxidant(s) compared to placebo or no treatment/standard treatment). This table evaluates the overall quality of the body of evidence for the main review outcomes (live birth, clinical pregnancy and adverse events), using GRADE criteria (study limitations: risk of bias, consistency of effect, imprecision, indirectness and publication bias). We have included an additional 'Summary of findings' table for the main review outcomes for the head‐to‐head comparison, evaluating those trials that look at one antioxidant versus another antioxidant. Two review authors, working independently, made judgements about evidence quality ('high', 'moderate', 'low' or 'very low').

Results

Description of studies

Results of the search

2013 version of the review

The search retrieved 2127 abstracts and titles, which we screened to identify trials that met our inclusion criteria. We retrieved the full texts of 67 trials for appraisal. Only one study (Bonakdaran 2012) was not published in English, with the full text in Persian; however, the English abstract contained enough information to show that it did not meet the inclusion criteria, and we therefore excluded it. Of the 67 studies assessed, we included 28 and excluded 39. A repeat search in April 2013 revealed seven studies (Carlomagno 2012; Choi 2012; Mohammadbeigi 2012; Rosalbino 2012; Salehpour 2012; Schachter 2007; Salem 2012) that we placed into the 'Awaiting classification' section of the review. We found 12 ongoing trials in searches of the clinical trial registers.

2017 Update

We assessed 926 abstracts (after 222 duplicates were removed) for inclusion from the title and abstract found in a search dated from April 2013 to September 2016. We assessed 39 of these papers in full text. One study was published in Persian (Mohammadbeigi 2012) and required translation (see Acknowledgements). We excluded 15 articles (14 studies) of the 39, and included 24 (23 studies). Of the latter, six were from the seven trials placed in 'Awaiting classification' in the original review, while Salem 2012 was excluded due to inappropriate intervention and control. For the 2017 update, four of the 12 previously ongoing trials are now included (Bentov 2014; Mohammadbeigi 2012; Unfer 2011; Youssef 2015). The conference abstract of the included study Aboulfoutouh 2011 in the original review became a secondary reference of Youssef 2015 in the update, and Rezk 2004, formerly an excluded study, is now included as a secondary reference of Rizk 2005. Pourghassem 2010 was found to be the same trial as the excluded Ardabili 2012. We excluded Pasha 2011 due to an ineligible population. We added two trials (NCT03023514; NCT02058212) after the search in September 2016, so eight trials were now ongoing (Fernando 2014; NCT01019785; NCT03023514; NCT02058212; IRCT201112148408N1; CTRI/2012/08/002943; NCT01782911; NCT01267604).

We included 23 trials in the 2017 update: Battaglia 1999; Bentov 2014; Brusco 2013; Carlomagno 2012; Cheraghi 2016; Choi 2012; Colazingari 2013; Daneshbodi 2013; Deeba 2015; El Refaeey 2014; Ismail 2014; Keikha 2010; Lesoine 2016; Maged 2015; Mohammadbeigi 2012; Pacchiarotti 2016; Panti Abubakar 2015; Polak de Fried 2013; Razavi 2015; Rosalbino 2012; Salehpour 2012; Schachter 2007; Valeri 2015.

Fifty trials were included in this updated review and 50 have been excluded.

2020 Update

For the 2020 update we assessed 1268 abstracts (after removing 262 duplicates), checking titles and abstracts for eligibility criteria. The articles were found in a search dated from 1st January 2013 to 12th September 2019. We retrieved 39 full‐text papers for further eligibility criteria and from this we excluded six articles (four studies) and included 31 articles (25 studies); one of these (Schillaci 2012) was found through handsearching references (See the PRISMA flow chart (Figure 1). All papers were in English.

For the current update one ongoing trial, Fernando 2014 became an included study (Fernando 2018). In addition to the seven ongoing trials from the 2017 update (NCT01019785; NCT03023514; NCT02058212; IRCT201112148408N1; CTRI/2012/08/002943; NCT01782911; NCT01267604), we added 26 new ongoing trials: ChiCTR1800019772; ChiCTR‐IPR‐15006369; EUCTR2015‐004233‐27‐IT; IRCT201009131760N9; IRCT201207156420N11; IRCT2012120311430N2; IRCT201306115942N2; IRCT20150831023831N2; IRCT201510266917N3; IRCT2016022821653N5; IRCT20160410027311N6; ISRCTN23488518; JPRN‐UMIN000016992; NCT01659788; NCT01665547; NCT01896492; NCT02239107; NCT02993588; NCT03085030; NCT03117725; NCT03306745; NCT03396380; NCT03476564; NCT04019899; PACTR201902584533870; TCTR20171109001.

We include 25 new studies in this review update: Al‐Alousi 2018; Behrouzi 2017; Caballero 2016; El Sharkwy 2019a; El Sharkwy 2019b; Espino 2019; Fernando 2018; Ghomian 2019; Hashemi 2017; Hefny 2018; Heidar 2019; Jahromi 2017; Jamilian 2018; Lu 2018; Mokhtari 2016; Mokhtari 2019; Mostajeran 2018; Rasekhjahromi 2018; Schillaci 2012; Sen Sharma 2017; Siavashani 2018; Taylor 2018; Tunon 2017; Xu 2018; Zadeh Modarres 2018.

Eight studies (Brusco 2013; Ciotta 2011; Colazingari 2013; Lesoine 2016; Pacchiarotti 2016; Papaleo 2009; Rosalbino 2012; Unfer 2011) were removed from the original review as they are now included in the Cochrane Review Inositol for subfertile women with polycystic ovary syndrome (Showell 2018).

Four pentoxifylline studies (Alborzi 2007; Aleyasin 2009; Balasch 1997; Creus 2008), were moved from the included category to excluded, as pentoxifylline is a prescription drug rather than an over‐the‐counter antioxidant supplement and therefore does not fit the inclusion criteria.

We now include 63 studies in this updated review (see Characteristics of included studies) and we exclude 58 (see Characteristics of excluded studies).

Included studies

Sixty‐three studies met the criteria for inclusion. Twenty were based in Iran (Behrouzi 2017; Cheraghi 2016; Daneshbodi 2013; Ghomian 2019; Hashemi 2017; Heidar 2019; Jahromi 2017; Jamilian 2018; Keikha 2010; Mohammadbeigi 2012; Mokhtari 2016; Mokhtari 2019; Mostajeran 2018; Rasekhjahromi 2018; Rashidi 2009; Razavi 2015; Salehpour 2009; Salehpour 2012; Siavashani 2018; Zadeh Modarres 2018), 10 in Egypt (Badawy 2006; El Refaeey 2014; El Sharkwy 2019a; El Sharkwy 2019b; Hefny 2018; Ismail 2014; Maged 2015; Rizk 2005; Nasr 2010; Youssef 2015). Eight were based in Italy (Battaglia 1999; Battaglia 2002; Carlomagno 2012; Gerli 2007; Lisi 2012; Rizzo 2010; Schillaci 2012; Valeri 2015), four in Turkey (Batioglu 2012; Cicek 2012; Eryilmaz 2011; Ozkaya 2011), three in Korea (Choi 2012; Kim 2006; Kim 2010), two in Spain (Espino 2019; Tunon 2017), in the USA (Taylor 2018; Westphal 2006), Argentina (Caballero 2016; Polak de Fried 2013) and China (Lu 2018; Xu 2018), and one each in the UK (Agrawal 2012), Hungary/Austria (Griesinger 2002), Mexico (Mier‐Cabrera 2008), Canada (Bentov 2014), Bangladesh (Deeba 2015), Nigeria (Panti Abubakar 2015), Israel (Schachter 2007), Australia (Fernando 2018), Iraq (Al‐Alousi 2018) and India (Sen Sharma 2017).

We tried to contact authors of all the included studies to obtain further details and clarification, but we could not obtain data for meta‐analysis from 24 trials (Al‐Alousi 2018; Caballero 2016; Carlomagno 2012; Choi 2012; Daneshbodi 2013; Deeba 2015; Ghomian 2019; Hashemi 2017; Hefny 2018; Heidar 2019; Jamilian 2018; Keikha 2010; Kim 2006; Kim 2010; Mohammadbeigi 2012; Mokhtari 2016; Ozkaya 2011; Rasekhjahromi 2018; Razavi 2015; Schillaci 2012; Siavashani 2018; Taylor 2018; Valeri 2015; Zadeh Modarres 2018), and one did not report on the outcomes included in this review (Salehpour 2009). In one trial (Gerli 2007) (see Table 3), only half of the participants declared that they wanted to become pregnant before the study began; we have therefore included this trial, but have not used the data in the meta‐analysis (see Characteristics of included studies).

1. Gerli 2007‐ data not included in meta‐analysis.

Outcome	Data	Notes
Clinical pregnancy rate; myo‐inositol + folic acid	4/23	Only 42 of the 92 women enrolled in this trial declared a desire to become pregnant
Clinical pregnancy rate; folic acid + placebo	1/19	‐
Miscarriage rate; myo‐inositol + folic acid	Miscarriage reported, but unknown whether from treatment or control	1 miscarriage occurred in the first trimester, but it is unknown from which group
Miscarriage rate; folic acid + placebo	Unknown	‐

Trial	Pregnancy in antioxidant group	Pregnancy in control group
Mier‐Cabrera 2008	0/16 (vitamins C + E), at follow‐up over 9 months 3/16	0/18 (placebo), at follow‐up over 9 months 2/18
Mohammadbeigi 2012	9/22 (vitamin D)	7/22 (placebo)
Razavi 2015	6/32 (selenium)	1/32 (placebo)
Al‐Alousi 2018	20/60 (omega)	15/58 (placebo)
Ghomian 2019	7/33 (NAC + CC)	5/33 (CC)
Heidar 2019	6/20 (selenium)	5/20 (placebo)
Siavashani 2018	5/20 (chromium)	4/20 (placebo)
Schillaci 2012	0/6 (myo‐inositol + 200 µg folic acid twice a day)	0/6 (400 µg folic acid once a day)

Antioxidant(s) compared to placebo or no treatment/standard treatment for female subfertility
Patient or population: women with subfertility Setting: Infertility clinics Intervention: Antioxidant(s) Comparison: placebo or no treatment/standard treatment
Outcomes	Relative effect (95% CI)	*Anticipated absolute effects^ (95% CI)**			Quality of the evidence (GRADE)	What happens
Outcomes	Relative effect (95% CI)	Without antioxidant(s)	With antioxidant(s)	Difference	Quality of the evidence (GRADE)	What happens
Live birth; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments) № of participants: 1227 (13 RCTs)	OR 1.81 (1.36 to 2.43)	19.0%	29.8% (24.2 to 36.3)	10.8% more (5.2 more to 17.3 more)	⊕⊝⊝⊝ VERY LOW^a,b,c	We are uncertain whether antioxidants improve live birth rate compared with placebo or no treatment/standard treatment.
Clinical pregnancy; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments) № of participants: 5165 (35 RCTs)	OR 1.65 (1.43 to 1.89)	18.8%	27.6% (24.8 to 30.4)	8.8% more (6.1 more to 11.6 more)	⊕⊕⊝⊝ LOW^a,d	Antioxidant(s) may improve clinical pregnancy rate, compared with placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments).
Adverse events ‐ Miscarriage № of participants: 3229 (24 RCTs)	OR 1.13 (0.82 to 1.55)	4.8%	5.4% (4 to 7.3)	0.6% more (0.8 fewer to 2.5 more)	⊕⊕⊝⊝ LOW^a,c	Antioxidant(s) may result in little to no difference in adverse events ‐ Miscarriage
Adverse events ‐ Multiple pregnancy № of participants: 1886 (9 RCTs)	OR 1.00 (0.63 to 1.56)	4.3%	4.3% (2.7 to 6.5)	0.0% fewer (1.6 fewer to 2.2 more)	⊕⊕⊝⊝ LOW^a,c	Antioxidant(s) may result in little to no difference in adverse events ‐ Multiple pregnancy
Adverse events ‐ Gastrointestinal disturbances № of participants: 343 (3 RCTs)	OR 1.55 (0.47 to 5.10)	2.4%	3.7% (1.2 to 11.2)	1.3% more (1.2 fewer to 8.8 more)	⊕⊕⊝⊝ LOW^a,c	Antioxidant(s) may result in little to no difference in adverse events ‐ Gastrointestinal disturbances
Adverse events ‐ Ectopic pregnancy № of participants: 404 (4 RCTs)	OR 1.40 (0.27 to 7.20)	0.6%	0.9% (0.2 to 4.3)	0.3% more (0.4 fewer to 3.7 more)	⊕⊕⊝⊝ LOW^a,c	Antioxidant(s) may result in little to no difference in adverse events ‐ Ectopic pregnancy
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).  CI: Confidence interval; OR: Odds ratio
GRADE Working Group grades of evidence High certainty: We are very confident that the true effect lies close to that of the estimate of the effect Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

Head‐to‐head antioxidants for female subfertility
Patient or population: women with subfertility Setting: Infertility clinics Intervention: Head‐to‐head antioxidants Comparison: Other antioxidant
Outcomes	Relative effect (95% CI)	*Anticipated absolute effects^ (95% CI)**			Quality of the evidence (GRADE)	What happens
Outcomes	Relative effect (95% CI)	With one antioxidant	With another antioxidant	Difference	Quality of the evidence (GRADE)	What happens
Live birth; type of antioxidant (natural conceptions and undergoing fertility treatments) ‐ Melatonin lower dose versus melatonin higher dose № of participants: 140 (2 RCTs)	OR 0.94 (0.41 to 2.15)	24.0%	22.9% (11.5 to 40.4)	1.1% fewer (12.5 fewer to 16.4 more)	⊕⊕⊝⊝ LOW^a,b	There was no clear evidence of a difference between the lower and higher doses of melatonin
Clinical pregnancy; type of antioxidant (natural conceptions and undergoing fertility treatments) ‐ N‐acetylcysteine versus L‐carnitine № of participants: 164 (1 RCT)	OR 0.81 (0.33 to 2.00)	14.6%	12.2% (5.4 to 25.5)	2.4% fewer (9.2 fewer to 10.9 more)	⊕⊝⊝⊝ VERY LOW^c,d	There was no clear evidence of a difference between N‐acetylcysteine versus L‐carnitine
Clinical pregnancy; type of antioxidant (natural conceptions and undergoing fertility treatments) ‐ Melatonin lower dose versus melatonin higher dose № of participants: 140 (2 RCTs)	OR 0.94 (0.41 to 2.15)	24.0%	22.9% (11.5 to 40.4)	1.1% fewer (12.5 fewer to 16.4 more)	⊕⊕⊝⊝ LOW^a,b	There was no clear evidence of a difference between the lower and higher doses of melatonin
Adverse events ‐ Miscarriage № of participants: 304 (3 RCTs)	OR 1.54 (0.42 to 5.67)	3.0%	4.6% (1.3 to 15.1)	1.6 more (1.7 fewer to 12.1 more)	⊕⊕⊝⊝ LOW^a,b	There were no miscarriages in either melatonin study (140 women) There was no clear evidence of a difference between N‐acetylcysteine versus L‐carnitine (164 women)
Adverse events ‐ Multiple pregnancy	There were no trials reporting multiple pregnancy
Adverse events ‐ Gastrointestinal disturbances	There were no trials reporting gastrointestinal disturbances
Adverse events ‐ Ectopic pregnancy Melatonin lower dose versus melatonin higher dose № of participants: 120 (1 RCT)	Not estimable, there were no ectopic pregnancies in either group				⊕⊝⊝⊝ VERY LOW ^{3 4}	There was no clear evidence of a difference between the lower and higher doses of melatonin
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).  CI: Confidence interval; OR: Odds ratio
GRADE Working Group grades of evidence High certainty: We are very confident that the true effect lies close to that of the estimate of the effect Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

Date	Event	Description
28 May 2020	New citation required and conclusions have changed	The removal of pentoxifylline studies, and those of myo‐inositol in women with polycystic ovary syndrome, and the addition of new studies has led to a change in the conclusions of this review.
28 May 2020	New search has been performed	We have removed from the review studies looking at myo‐inositol for women with polycystic ovary syndrome, as they are now included in another published Cochrane Review (Showell 2018) (Ciotta 2012; Papaleo 2008; Raffone 2010). We moved four formerly‐included pentoxifylline studies to excluded studies, as pentoxifylline is a prescription drug rather than an over‐the‐counter antioxidant supplement (Alborzi 2007; Aleyasin 2009; Balasch 1997; Creus 2008).
16 October 2017	Amended	Some references updated and corrected
28 June 2017	New citation required and conclusions have changed	With the addition of new studies data now show an association between the use of antioxidants and live birth and clinical pregnancy.
28 June 2017	New search has been performed	Updated. Twenty‐three new trials added, making a total of 50 trials now included in this updated review. New studies added:Battaglia 1999; Bentov 2014; Brusco 2013; Carlomagno 2012; Cheraghi 2016; Choi 2012; Colazingari 2013; Daneshbodi 2013; Deeba 2015; El Refaeey 2014; Ismail 2014; Keikha 2010; Lesoine 2016; Maged 2015; Mohammadbeigi 2012; Pacchiarotti 2016; Panti Abubakar 2015; Polak de Fried 2013; Razavi 2015; Rosalbino 2012; Salehpour 2012; Schachter 2007; Valeri 2015.
22 April 2008	Amended	Converted to new review format.
9 August 2007	New citation required and major changes	Substantive amendment

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Live birth; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments)	13	1227	Odds Ratio (M‐H, Fixed, 95% CI)	1.81 [1.36, 2.43]
1.1.1 Placebo	7	628	Odds Ratio (M‐H, Fixed, 95% CI)	1.89 [1.18, 3.03]
1.1.2 No treatment	6	599	Odds Ratio (M‐H, Fixed, 95% CI)	1.77 [1.22, 2.56]
1.2 Live birth; type of antioxidant	13	1227	Odds Ratio (M‐H, Fixed, 95% CI)	1.81 [1.36, 2.43]
1.2.1 N‐acetyl‐cysteine	1	60	Odds Ratio (M‐H, Fixed, 95% CI)	3.00 [1.05, 8.60]
1.2.2 L‐arginine	1	37	Odds Ratio (M‐H, Fixed, 95% CI)	0.43 [0.09, 2.09]
1.2.3 CoQ10	2	225	Odds Ratio (M‐H, Fixed, 95% CI)	1.50 [0.78, 2.88]
1.2.4 Vitamin D	1	52	Odds Ratio (M‐H, Fixed, 95% CI)	0.79 [0.21, 3.02]
1.2.5 Vitamin B complex	1	102	Odds Ratio (M‐H, Fixed, 95% CI)	2.07 [0.93, 4.57]
1.2.6 Combined antioxidants	3	378	Odds Ratio (M‐H, Fixed, 95% CI)	2.59 [1.52, 4.40]
1.2.7 Vitamin E	1	103	Odds Ratio (M‐H, Fixed, 95% CI)	1.43 [0.50, 4.10]
1.2.8 Melatonin	3	270	Odds Ratio (M‐H, Fixed, 95% CI)	1.60 [0.68, 3.76]
1.3 Live birth; indications for subfertility	11		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.3.1 Polycystic ovary syndrome	3	362	Odds Ratio (M‐H, Fixed, 95% CI)	3.34 [1.90, 5.86]
1.3.2 Tubal subfertility	1	37	Odds Ratio (M‐H, Fixed, 95% CI)	0.43 [0.09, 2.09]
1.3.3 Varying indications	3	338	Odds Ratio (M‐H, Fixed, 95% CI)	1.70 [1.02, 2.83]
1.3.4 Unexplained subfertility	2	133	Odds Ratio (M‐H, Fixed, 95% CI)	1.50 [0.60, 3.72]
1.3.5 Poor ovarian reserve	2	266	Odds Ratio (M‐H, Fixed, 95% CI)	1.75 [0.83, 3.67]
1.4 Live birth; IVF/ICSI	9	806	Odds Ratio (M‐H, Fixed, 95% CI)	1.36 [0.96, 1.93]
1.5 Clinical pregnancy; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments)	35	5165	Odds Ratio (M‐H, Fixed, 95% CI)	1.65 [1.43, 1.89]
1.5.1 Placebo	17	3292	Odds Ratio (M‐H, Fixed, 95% CI)	1.70 [1.42, 2.05]
1.5.2 No treatment/standard treatment	19	1873	Odds Ratio (M‐H, Fixed, 95% CI)	1.57 [1.28, 1.94]
1.6 Clinical pregnancy; type of antioxidant	35	5165	Odds Ratio (M‐H, Fixed, 95% CI)	1.65 [1.43, 1.89]
1.6.1 N‐acetylcysteine	8	1590	Odds Ratio (M‐H, Fixed, 95% CI)	1.36 [1.05, 1.77]
1.6.2 Combined antioxidants	5	689	Odds Ratio (M‐H, Fixed, 95% CI)	1.90 [1.33, 2.70]
1.6.3 Melatonin	7	678	Odds Ratio (M‐H, Fixed, 95% CI)	1.66 [1.12, 2.47]
1.6.4 Vitamin E	1	103	Odds Ratio (M‐H, Fixed, 95% CI)	1.43 [0.50, 4.10]
1.6.5 Ascorbic acid	2	899	Odds Ratio (M‐H, Fixed, 95% CI)	0.91 [0.66, 1.25]
1.6.6 L‐arginine	2	71	Odds Ratio (M‐H, Fixed, 95% CI)	1.05 [0.32, 3.46]
1.6.7 Myo‐inositol plus folic acid	1	94	Odds Ratio (M‐H, Fixed, 95% CI)	1.24 [0.50, 3.06]
1.6.8 CoQ10	4	397	Odds Ratio (M‐H, Fixed, 95% CI)	2.49 [1.50, 4.13]
1.6.9 L‐carnitine	2	450	Odds Ratio (M‐H, Fixed, 95% CI)	11.14 [5.70, 21.81]
1.6.10 Vitamin D	2	92	Odds Ratio (M‐H, Fixed, 95% CI)	0.83 [0.25, 2.76]
1.6.11 Vitamin B complex	1	102	Odds Ratio (M‐H, Fixed, 95% CI)	1.94 [0.82, 4.58]
1.7 Clinical pregnancy; indications for subfertility	31		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.7.1 Polycystic ovary syndrome	15	1908	Odds Ratio (M‐H, Fixed, 95% CI)	4.24 [3.23, 5.56]
1.7.2 Unexplained	4	997	Odds Ratio (M‐H, Fixed, 95% CI)	0.84 [0.61, 1.16]
1.7.3 Tubal subfertility	2	71	Odds Ratio (M‐H, Fixed, 95% CI)	1.05 [0.32, 3.46]
1.7.4 Varying indications	6	1135	Odds Ratio (M‐H, Fixed, 95% CI)	1.14 [0.85, 1.52]
1.7.5 Poor responders	1	65	Odds Ratio (M‐H, Fixed, 95% CI)	1.88 [0.64, 5.47]
1.7.6 Poor ovarian reserve	2	266	Odds Ratio (M‐H, Fixed, 95% CI)	1.70 [0.86, 3.37]
1.7.7 Endometriosis	1	280	Odds Ratio (M‐H, Fixed, 95% CI)	1.19 [0.71, 1.98]
1.8 Clinical pregnancy; IVF/ICSI	18	2341	Odds Ratio (M‐H, Fixed, 95% CI)	1.15 [0.95, 1.40]
1.9 Adverse events	27		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.9.1 Miscarriage	24	3229	Odds Ratio (M‐H, Fixed, 95% CI)	1.13 [0.82, 1.55]
1.9.2 Multiple pregnancy	9	1886	Odds Ratio (M‐H, Fixed, 95% CI)	1.00 [0.63, 1.56]
1.9.3 Gastrointestinal disturbances	3	343	Odds Ratio (M‐H, Fixed, 95% CI)	1.55 [0.47, 5.10]
1.9.4 Ectopic pregnancy	4	404	Odds Ratio (M‐H, Fixed, 95% CI)	1.40 [0.27, 7.20]
1.9.5 Headache	2	330	Odds Ratio (M‐H, Fixed, 95% CI)	0.89 [0.45, 1.75]
1.9.6 Congenital (missing kidney)	1	160	Odds Ratio (M‐H, Fixed, 95% CI)	1.02 [0.04, 25.46]
1.9.7 Low birth weight < 2.500 g	1	160	Odds Ratio (M‐H, Fixed, 95% CI)	0.11 [0.00, 2.74]
1.9.8 Preterm birth	2	220	Odds Ratio (M‐H, Fixed, 95% CI)	1.31 [0.17, 9.93]
1.9.9 Placenta praevia	1	160	Odds Ratio (M‐H, Fixed, 95% CI)	1.02 [0.04, 25.46]
1.9.10 Pre‐eclampsia	1	160	Odds Ratio (M‐H, Fixed, 95% CI)	1.71 [0.08, 36.35]
1.9.11 Fatigue	1	160	Odds Ratio (M‐H, Fixed, 95% CI)	1.86 [0.75, 4.62]
1.9.12 Ovarian hyperstimulation syndrome (OHSS)	1	150	Odds Ratio (M‐H, Fixed, 95% CI)	Not estimable

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Live birth; type of antioxidant (natural conceptions and undergoing fertility treatments)	2	140	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.41, 2.15]
2.1.1 Melatonin lower dose versus melatonin higher dose	2	140	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.41, 2.15]
2.2 Live Birth; indications for subfertility	2		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.2.1 Unexplained subfertility	1	20	Odds Ratio (M‐H, Fixed, 95% CI)	1.00 [0.15, 6.77]
2.2.2 Varying Indications	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	0.93 [0.37, 2.32]
2.3 Live Birth; IVF/ICSI	2	140	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.41, 2.15]
2.4 Clinical pregnancy; type of antioxidant (natural conceptions and undergoing fertility treatments)	3		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.4.1 N‐acetylcysteine versus L‐carnitine	1	164	Odds Ratio (M‐H, Fixed, 95% CI)	0.81 [0.33, 2.00]
2.4.2 Melatonin lower dose versus melatonin higher dose	2	140	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.41, 2.15]
2.5 Clinical pregnancy; indications for subfertility	3		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.5.1 Polycystic ovary syndrome	1	164	Odds Ratio (M‐H, Fixed, 95% CI)	0.81 [0.33, 2.00]
2.5.2 Unexplained subfertility	1	20	Odds Ratio (M‐H, Fixed, 95% CI)	1.00 [0.15, 6.77]
2.5.3 Varying indications	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	0.93 [0.37, 2.32]
2.6 Clinical pregnancy; IVF/ICSI	2	140	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.41, 2.15]
2.7 Adverse events	3		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.7.1 Miscarriage	3	304	Odds Ratio (M‐H, Fixed, 95% CI)	1.54 [0.42, 5.67]
2.7.2 Ectopic pregnancy	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	Not estimable
2.7.3 Congenital (missing kidney)	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	1.53 [0.06, 38.36]
2.7.4 Low birth weight < 2.500 g	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	Not estimable
2.7.5 Birth between 34 and 37 weeks	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	0.49 [0.03, 8.10]
2.7.6 Placenta praevia	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	1.53 [0.06, 38.36]
2.7.7 Pre‐eclampsia	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	0.49 [0.03, 8.10]

*Study characteristics*
Methods	Prospective randomised trial
Participants	Women attending a teaching hospital fertility clinic undergoing ovulation induction for timed intercourse (N = 58). Mean age 32.2 years (range 19 to 40) Inclusion criteria: anovulatory infertility, at least 12 months of unexplained infertility, PCOS, hypothyroidism or minimal endometriosis Exclusion criteria: women whose partners had semen abnormalities and those who had been on multivitamins (except folate) 6 weeks before recruitment Women with tubal disease, moderate and severe endometriosis, medical disorders or haemoglobinopathies; smokers, those with excessive alcohol intake or BMI < 19 or > 34 kg/m²
Interventions	1. Multiple micronutrients (MMN): (n = 30) 1 tablet a day until completion of study (3 treatment cycles). Women who became pregnant could continue if they wished. These micronutrients consist of thiamine, riboflavin, niacin B3, vitamins B6 and B12, folate, vitamins C, A and D, calcium, phosphorus, magnesium, sodium, potassium, chloride, iron, zinc, copper, selenium, iodine, vitamin E, vitamin K, L‐arginine, inositol, N‐acetyl‐cysteine, biotin, pantothenic acid Mean age = 32.2 ± 0.65 2. Folic acid (n = 28): 1 tablet a day. Mean age = 32.5 ± 0.83 Women underwent ovulation induction with clomiphene citrate or human menopausal gonadotropin approximately 4 weeks after starting MMN or folic acid and continued until end of study, which was 3 cycles even if pregnancy was attained.
Outcomes	Clinical pregnancy Ongoing pregnancy Miscarriage Ectopic pregnancy
Notes	2 women did not complete the study－1 from each group. Reasons given: 1 woman in the control group stopped because she wanted to take the micronutrients, and 1 in the treatment group stopped because of nausea Trial is self‐funded. Author stated in an email received 13th February that the trial was not funded. Recruited between Febuary and August 2009 Trial registration number: Unknown Location: London UK Informed consent Ethical approval Sample size power calculation performed ITT performed Emailed author 12th January 2012 about whether the women had IUI or timed intercourse. Author replied on 7th February 2012 saying that all women underwent timed intercourse, not IUI. This email also gave adverse event data (miscarriage and ectopic pregnancy data) for the first cycle. Dr Agrawal is also currently recruiting for a new trial. Emailed author on 9th August 2012 asking about any live birth data. Author replied saying that live birth data were unavailable.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Third party randomization ... was carried out through the research and development department of the University College London and the Royal Free Hospitals using stratification..." "Participants were randomly allocated". Comment: Email sent 12th January 2012 asking for methods of randomisation. Author replied 13th February 2012 saying, "the subjects were randomised into 2 groups through computer randomisation".
Allocation concealment (selection bias)	Low risk	Quote: "Third party randomisation and allocation concealment was carried out through the research and development department of the University College London and the Royal Free Hospitals using stratification and numbered envelopes".
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Women, caregivers and investigators were blinded to the treatment allocation".
Incomplete outcome data (attrition bias) All outcomes	Low risk	ITT was performed and explanations given for the 2 dropouts (1 from each group)
Selective reporting (reporting bias)	Unclear risk	Trial registration number unknown. Outcomes, including clinical pregnancy and live birth were stated in the text, are reported.
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Randomised controlled trial
Participants	Women attending a fertility clinic, undergoing ICSI (N = 118 randomised) Inclusion criteria: Women aged between 20 and 40 years, mean age for all participants 29.37 years. BMI between 18 and 34.99 kg/m², 1st or 2nd cycle of ICSI, and fresh sperm sample (not aspirated) Exclusion criteria: Women who have medical disorders e.g. diabetes mellitus, hypertension or thyroid diseases, sperm collection from epididymal aspiration, PESA and TESE, frozen sperm, consumption of any medications in the last 12 weeks that may influence hormonal assay, history of any diet in the previous 3 months, tobacco and alcohol consumption, and supplementation of n‐3 PUFAs in the past 3 months
Interventions	1. The women of group A were given omega‐3 for 8 weeks, before starting the ICSI protocol (N = 60). 1000 mg x 1 capsule every day composed of 180 mg eicosapentaenoic acid (EPA) and 120 mg docosahexaenoic acid (DHA). Mean age = 29.22 ± 5.74 2. Placebo for 8 weeks, before starting the ICSI protocol (N = 58). Capsule contains 500 mg paraffin manufactured by Alzahravi Pharmacology Company. Mean age = 29.60 ± 5.34
Outcomes	Embryo quality Number of follicles Number of oocytes Fertilisation rates Ratio of follicle/retrieved oocytes Number of metaphase II oocytes Number of grade I embryos Pregnancy
Notes	3 women did not complete the study－1 from the intervention and 2 from the control, reasons not given Location: Al‐Sadr Teaching Hospital/ Fertility Center/ IVF Department in Najaf Al‐Ashraf City, Iraq Timeframe: from January 2017 to February 2018 Trial registration number: unknown Informed consent: unknown Ethical approval: unknown Sample size power calculation performed Funding: Unknown Conflict of interests: unknown ITT not performed The outcome pregnancy is possibly biochemical; there is no definition but mention "pregnancy test", positive or negative Author emailed 14 January 2020 with questions on pregnancy definition, other clinical outcomes, trial registration number and RoB details Author email: tk_says@yahoo.com
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Unknown methods of randomisation
Allocation concealment (selection bias)	Unclear risk	Unknown methods of allocation concealment
Blinding (performance bias and detection bias) All outcomes	Low risk	Outcome group: Double‐blind Quote: " Neither the researcher nor women knew which group takes then‐3 or placebo till the end of the research. All The placebo and omega‐3 capsules look similar and cannot be distinguished from each other (same form of package, same shape, same size and colour)"
Incomplete outcome data (attrition bias) All outcomes	Low risk	3 women dropped out after randomisation – groups explained but reasons not given
Selective reporting (reporting bias)	Unclear risk	Trial registration unavailable
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Prospective randomised double‐blind controlled trial
Participants	Women attending a fertility outpatient clinic for management of unexplained fertility problems (n = 804) Mean age: Treatment group: 27.9 years; Control group 28.1 years Inclusion criteria: All women had at least 1 year of marriage without conception, unexplained subfertility and normal ovulating cycles; tubes were patent Exclusion criteria: any known reason for subfertility Timed intercourse
Interventions	1. N‐acetyl‐cysteine 1200 mg: 1 tablet a day plus clomiphene citrate 50 mg: 1 tablet twice a day for 5 days, starting on day 2 of the cycle (n = 404) 2. Placebo plus clomiphene citrate: 50 mg 1 tablet twice a day (n = 400) Duration of treatment: 1 cycle Timed intercourse
Outcomes	Number and size of follicles Hormonal profiles Endometrial thickness Clinical Pregnancy Miscarriage Multiple pregnancy No loss to follow‐up
Notes	Conducted in 1 centre in Mansoura, Egypt. Ethical approval and informed consents obtained Trial ran from October 2003 to April 2005 Funding source not reported Contacted author 13th February 2013 regarding methods of randomisation. Author replied 11 February 2013 giving data for multiple pregnancy and miscarriage.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No description of sequence generation apart from: Quote: "Patients were allocated randomly to either the trial group".
Allocation concealment (selection bias)	Low risk	Sealed, opaque, sequentially‐numbered, identical envelopes were used
Blinding (performance bias and detection bias) All outcomes	Low risk	Participants, investigators, outcome assessor and clinicians were blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	No withdrawals or dropouts
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. Outcomes stated in the text－multiple pregnancy and miscarriage－reported on, although not initially stated as outcomes of interest
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Double‐blind placebo‐controlled randomised trial
Participants	IVF/ICSI patients (N = 39) Inclusion criteria: infertility requiring IVF–ICSI and age 35 – 43, mean age; CoQ10 39.0 ± 0.79 and placebo 39.1 ± 0.52 Exclusion criteria: body mass index (BMI) >38 kg/m2; early follicular phase (day 2 – 4) serum FSH level >20 mIU/mL; abnormal uterine cavity as evidenced by sonohysterogram or hysterosalpingography; any current use of systemic steroid medication or any infertility treatment within 3 months of study enrolment; any contraindication to being pregnant and carrying a pregnancy to term; contraindication for the use of CoQ10, superfact, menopur, hCG, estrase, and progesterone suppositories; any ovarian or abdominal abnormality that may interfere with adequate TVS evaluation; absence of 1 or both ovaries; clinically relevant systemic disease (e.g. insulin‐dependent diabetes, adrenal dysfunction, organic intracranial lesion, PCOS, hyperprolactinemia, or hypothalamic tumor) or serious illness (neoplasia); history (within past 12 months) or current abuse of alcohol or drugs; administration of any investigational drugs within 3 months before the study enrolment; any medical condition that may interfere with the absorption, distribution, metabolism, or excretion of the study drugs; gastrointestinal diseases; malabsorption syndromes; and liver dysfunction; unexplained gynaecological bleeding; ejaculated sperm not sufficient for ICSI; abnormal controlled ovarian hyperstimulation (COH) screening blood done for both partners, including prolactin, thyroid stimulating hormone, HIV serology, hepatitis B and C serology, rubella, group and screen, and syphilis serology before participation in the study; the concurrent use of any of the following drugs: daunorubicin, doxorubicin, blood pressure medications, warfarin, timolol, atorvastatin, cerivastatin, lovastatin, pravastatin, simvastatin, gemfibrozil, tricyclic antidepressant medications (including amitriptyline, amoxapine, clomipramine, desipramine, doxepin, imipramine, nortriptyline, protriptyline, and trimipramine), multivitamins, or any vitamin supplementation except folic acid
Interventions	1. CoQ10 600 mg: 1 tablet a day with breakfast (N = 17) 2. Placebo ‐ identical capsules containing rice oil and starch (N = 22) Duration of treatment up to 3 cycles if pregnancy did not occur. All participants took either CoQ10 or placebo for 2 months. On day 3 of the following cycle, they started ovarian stimulation for IVF while continuing the consumption of the supplements.
Outcomes	Primary outcome: number of euploid eggs per retrieval Secondary outcome: cumulative pregnancy rate per retrieval and cumulative livebirth rate per retrieval
Notes	12 (5 dropouts) CoQ10 group and 15 (7 dropouts) in the placebo completed the study and 10 in the CoQ10 and 14 of the placebo group completed an IVF/ICSI cycle. Overall there were 15 dropouts from recruitment until the end of the study; 6 women withdrew from the study for personal reasons, 3 for conceiving spontaneously, 2 for poor compliance, 1 for failing to achieve the target BMI, and 3 because of poor ovarian response Participant enrolment to the study began in 2010 and was terminated in June 2012 before sample size reached, due to a paper published in May 2012 by Levin et al describing the negative effects of polar body biopsy on embryogenesis. In the CoQ10 group, 30.8% of the women were treated with the long luteal GnRH agonist protocol, compared with 7.7% in the placebo group. The rest of the participants in both groups were treated with the short microdose flare protocol 2 centres Toronto, Canada Trial registration no: NCT01048385 Informed consent: yes Ethics approval: yes Funding; Ferring Pharmaceuticals provided Menopur Conflict of interests; one of the authors has a consultancy role with Fertility Neutraceuticals involved in the manufacturing and distribution of CoQ10 Email sent to author regarding live birth, clinical pregnancy, dropouts and allocation concealment on 24th November 2015 'bentov@lunenfeld.ca', no reply
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients were assigned in chronological order according to the day of study enrolment to a computer‐generated randomization"
Allocation concealment (selection bias)	Unclear risk	Quote: "Each enrolled participant received a pre‐assigned package containing either placebo or CoQ10 for the duration of the study".
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "The study was a double blind, placebo‐controlled, randomized trial". "Both the physician and the patient were blinded regarding assignment of the patients".
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "At the point the study was terminated (June 2012), we had recruited a total of 39 patients who were evaluated and randomized (17 to the CoQ10 group and 22 to the placebo group). Only 27 had started the treatment with the supplements (12 of the CoQ10 group and 15 of the placebo group). In all, 24 patients completed the treatment cycle and had a polar body biopsy (PBBX) and embryo transfer done (10 of the CoQ10 group and 14 of the placebo group). Six patients withdrew from the study for personal reasons, three for conceiving spontaneously, two for poor compliance, one for failing to achieve the target BMI, and three because of poor ovarian response."
Selective reporting (reporting bias)	Low risk	Both primary and secondary outcomes, including live birth, were reported in the Methods were reported in the Results. Protocol available.
Other bias	High risk	Quote: "However, because of the premature termination of the study, the CoQ10 group had only one‐third and the control group half of the target number". Comment: Early termination of trial for embryo safety reasons may cause an overestimation of the effect of the intervention

*Study characteristics*
Methods	Double‐blind RCT
Participants	Women undergoing ICSI (N not stated)
Interventions	1. Myo‐inostol 4 g and folic acid 400 μg: 1 tablet of each a day (n not stated) 2. Folic acid 400 μg: 1 tablet a day (n not stated) Taken for 3 months before ICSI and throughout pregnancy
Outcomes	Total rFSH units Number of stimulation days Fertilisation and cleavage rate Embryo quality Biochemical pregnancy rate Clinical pregnancy rate
Notes	Conducted in Italy, study dates not reported Conference abstract; percentages given but no total participant numbers available Funding by an institutional grant. An author was an employee of a pharmaceutical company Email sent to author 24th November 2015 Gianfranco.carlomagno@gmail.com; no reply.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly assigned to two groups; MI treated or placebo"
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Double blind"
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not mentioned
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available
Other bias	Unclear risk	Conference abstract ‐ baseline numbers unclear

*Study characteristics*
Methods	Prospective randomised placebo‐controlled pilot trial
Participants	Infertile Iranian women with PCOS, aged from 25 ‐ 35 years, undergoing ICSI treatment (N = 80) Inclusion criteria: Women who met the Rotterdam criteria for PCOS Exclusion criteria: Hypersensitivity to either MET (metformin) or NAC, infertility factors other than anovulation, male infertility, pelvic organic pathologies, congenital adrenal hyperplasia, thyroid dysfunction, Cushing’s syndrome, hyperprolactinaemia, androgen‐secreting neoplasia, diabetes mellitus, consumption of medications affecting carbohydrate metabolism and hormonal analogues other than progesterone 2 months prior to enrolment in the study and severe hepatic or kidney disease
Interventions	4 groups (N = 20 in each, 5 dropouts from each) 1. Placebo oral rehydration salts; 3 times a day 2. Metformin 500 mg: 1 tablet 3 times a day 3. NAC 600 mg: 1 tablet 3 times a day 4. Metformin 500 mg: 1 tablet 3 times a day + NAC 600 mg: 1 tablet 3 times a day All treatments were administered for 6 weeks
Outcomes	Oocyte and embryo quality Endocrine parameters Clinical pregnancy Side effects
Notes	Location: Iran Timeframe: study ran from July 2012 to February 2013 Trial registration number: IRCT201204159476N1 Informed consent: yes Ethical approval: yes Sample size power calculation: unknown Funding: Arak University Conflict of interests: authors declare no conflicts of interest ITT: No, 15 women per group were analysed Author email: M‐soleimani@araku.ac.ir Author emailed regarding RoB, live birth and miscarriage information; no reply. Author emailed again 15.01.20.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	State "random" but method not described
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding (performance bias and detection bias) All outcomes	High risk	Double‐blinded placebo‐controlled, but the placebo group received oral rehydration salts, which are usually in solution, while the treatments were tablets
Incomplete outcome data (attrition bias) All outcomes	High risk	Dropouts accounted for, but > 25% dropout
Selective reporting (reporting bias)	Low risk	Trial registration number available. Clinical pregnancy reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Prospective, randomised controlled trial
Participants	Infertile women with PCOS (N = 100) undergoing IVF/ICSI
Interventions	1. Calcium 400 mg + vitamin D 1000 IU: 1 of each tablet a day (N = 50) 2. Placebo (N = 50) Given on the starting day of OC pretreatment, followed by controlled ovarian stimulation (COS) using GnRH antagonist for IVF/ICSI. Calcium 400 mg/day with vitamin D 1000 IU/d or placebo was administered once daily from the starting day of OC to the day of human chorionic gonadotropin (hCG) injection
Outcomes	Total dose and days of rhFSH administered Numbers of retrieved, mature and fertilised oocytes, and grade 1 or 2 embryos FF TNF‐a and IL‐6 concentrations at oocyte retrieval Embryo implantation rate Clinical pregnancy rate Miscarriage rate
Notes	Korea, study dates not reported Conference abstract Funding source not reported No data for clinical pregnancy or live birth stated in the conference abstract; emailed co‐author CH Kim; chnkim@amc.seoul.kr, asking about risk of bias, any full publication of the trial and whether they had any clinical pregnancy and miscarriage data. No reply.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "infertile patients with PCOS were randomized"
Allocation concealment (selection bias)	Unclear risk	Unknown
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unknown
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unknown
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available, clinical pregnancy and miscarriage rate reported
Other bias	Unclear risk	Conference abstract ‐ unclear baseline characteristics

*Study characteristics*
Methods	Randomised double‐blind placebo‐controlled clinical trial
Participants	Overweight and obese women with PCOS, (N = 84) Inclusion criteria: PCOS diagnostic criteria based on the Rotterdam Criteria, age between 20 and 40 years, and BMI of 25 ‐ 40 Exclusion criteria: Metabolic disease, thyroid disease, hyperprolactinaemia, hypercortisolaemia, congenital adrenal hyperplasia, Cushing’s syndrome, pituitary disorder, neoplasm, renal and liver diseases, history of intake of any drug during the last 3 months that may affect the insulin sensitivity or hormonal profile such as: oral contraceptives, glucocorticoids, ovulation induction agents, antidiabetic and anti‐obesity drugs, oestrogenic, antiandrogenic or anti‐hypertensive medication, being on any diet in the last 6 months, any addiction to tobacco and alcohol, taking omega‐3 supplement in the last 3 months, menopause, allergy to sea foods, and the use of anti‐coagulant medicine. Women were excluded if they needed OCP for treatment, were not willing to be in the study, did not obey the protocols of the study, or could not digest more than 20% of supplements
Interventions	1. Oral omega 3; 3 capsules of omega‐3 every day for 8 weeks. Each capsule of omega‐3 contained 180 mg EPA and 120 mg DHA. Mean age was 26.9 ± 5.9 years 2. Placebo; included 1 g paraffin (Zahravi, Iran), Mean age was 26.9 ± 5.0 years Duration of treatment; 8 weeks
Outcomes	Biochemical markers (FSH, LH, prolactin)
Notes	17 October 2012 we added the full‐text Nadjarzadeh 2015, becoming the primary reference. The original report for this study was a conference abstract, Daneshbodi 2013. We were able to additional data to the table of characteristics and risk of bias, but we retained the original name of the study as Daneshbodi 2013 Conducted in Iran, study dates not reported Iranian Registry of Clinical Trial (Registry no IRCT2012071410281N1 and IRCT201112318564N1) Funding source not reported, authors state no conflict of interests Author emailed for RoB and pregnancy data. No reply.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: Methods unknown Quote: “Subjects were randomly divided in to two groups of A and B to reduce the bias.”
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blinded (placebo control)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "In this study, one of the participants became pregnant and left the study. 5 participants dropped out because of taking less than 20% of our capsules. The remaining 78 participants completed the study. Finally, 78 people (92.8%) among the patients, 39 patients in the group receiving omega‐3 and 39 patients in the group receiving placebo, finished the eight week trial."
Selective reporting (reporting bias)	Unclear risk	Trial registration number is available, but no pregnancy outcomes reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Prospective randomised controlled trial
Participants	Women with clomiphene‐citrate‐resistant PCOS attending a fertility outpatient clinic Timed intercourse (N = 110) Inclusion criteria: diagnosis of PCOS. All women were previously treated with 150 mg clomiphene citrate daily for 5 days per cycle, for 2 or 3 cycles with persistent anovulation or ovulate with very thin endometrium (< 5 mm). All women had patent fallopian tubes Exclusion criteria: women with hyperprolactinaemia, hypercorticism and thyroid dysfunction and women receiving medications such as cholesterol‐lowering drugs, beta‐blockers and tricyclic antidepressants
Interventions	1. CoQ10 60 mg: 3 capsules a day + clomiphene citrate 150 mg: 1 tablet a day, from cycle days 2 – 6 starting on cycle day 2 and until the day of hCG administration (N = 55) 2. Clomiphene citrate 150 mg: 1 tablet a day from cycle day 2 for 5 days (N = 55) The mean duration of CoQ10 treatment in the 1st cycle was 16.2 ± 2.1 days and in the 2nd cycle 17.1 ± 2.9 days
Outcomes	Primary outcomes: number of growing and mature follicles, serum oestradiol, serum progesterone, ovulation rate, endometrial thickness Secondary outcomes: clinical pregnancy (ultrasound visualisation of gestational sac with pulsating fetal pole) and miscarriage (spontaneous termination of a clinical pregnancy before 20 weeks of gestation)
Notes	Sample size calculation done 4 dropouts from the intervention and 5 from the control group Egypt Trial duration January 2010 to January 2013 The study was approved by the departmental ethical committee and all participants gave informed consent before inclusion in the trial (committee reference no. 231, approved December, 12 2009) This trial is registered at ClinicalTrials.gov (ID NCT01910766) Email to author regarding live birth data and allocation concealment sent 26th November 2015. No reply. Endometrial thickness; significant difference in favour of the treatment group vs control
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients were randomly allocated using a computer generated random table"
Allocation concealment (selection bias)	Low risk	Quote: "sealed envelopes" "Allocation process was done by a third party (nurse)"
Blinding (performance bias and detection bias) All outcomes	High risk	Quote: "The physicians monitoring the cycles were blinded to the protocol of each group"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropouts accounted for from each arm
Selective reporting (reporting bias)	Low risk	Trial registration number available. All outcomes were reported as stated in the Methods, including clinical pregnancy and miscarriage
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Parallel double‐blind randomised controlled clinical trial
Participants	Women with CC‐resistant PCOS attending the infertility clinic Ovulation induction (N = 164) Inclusion criteria: Age 18 – 40 years; infertility for > 1 year; PCOS, defined by the revised Rotterdam 2003 criteria 7 as the presence of 2 of 3 features (oligo and/or anovulation, clinical and/or biochemical signs of hyperandrogenism, and polycystic ovary); and CC resistance, defined as failure to achieve adequate follicular maturation after 3 consecutive induction cycles with CC at a dose of 150 mg/day for 5 days. Exclusion criteria: Other causes of infertility (e.g. male or tubal factor), endocrine disorders such as thyroid dysfunction and hyperprolactinaemia, and hormonal treatment or intake of any medications affecting carbohydrate or lipid metabolism in the 3 months before the study
Interventions	1. 150 mg/day of CC from day 3 until day 7 of the menstrual cycle, plus 600 mg of oral N‐acetylcysteine (a sachet of powder for dilution in water) and a placebo capsule similar to the L‐carnitine capsule, 3 times daily. Mean age 26.6 ± 1.5 (N = 82) 2. 150 mg/day of CC from day 3 until day 7 of the menstrual cycle, plus 3 g of oral L‐carnitine and placebo sachets containing an oral rehydration solution specifically designed to look similar to those containing N‐acetylcysteine Mean age 26.2 ± 2.8 (N = 82) Treatment period: 3 months
Outcomes	Clinical pregnancy Ovulation Metabolic profile (insulin resistance markers and lipid profile)
Notes	Location: Department of Obstetrics and Gynecology Faculty of Medicine, Zagazig University Egypt Timeframe: between 01 January 2017 and 31 March 2018 Trial registration number: NCT03164421 Informed consent: yes Ethical approval: from Zagazig University Sample size power calculation: yes Funding: unknown Conflict of interests: no conflicts stated ITT: no Author email: Ibrahimsharkwy@yahoo.com Emailed author 15 January 2020 to ask if they have live birth data or any other adverse event data. No reply as of 26 August 2020.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “Consenting eligible women were randomly allocated to receive either CC plus N‐acetylcysteine or CC plus l‐carnitine via computer generated randomization tables that guaranteed a 1:1 distribution of women between the two study groups.” (page 61)
Allocation concealment (selection bias)	Low risk	The allocations were concealed in opaque, sealed, and serially‐numbered envelopes. The randomisation code was known only to the pharmacist who dispensed the medications (page 61)
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: “The women and the physicians were blind to the allocation.” (page 61)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition accounted for. Quote: “Two women in the l‐carnitine group were subsequently lost to follow‐up and excluded from the analysis”
Selective reporting (reporting bias)	Low risk	Trial registration number is available, clinical pregnancy reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Parallel double‐blinded randomised controlled clinical trial
Participants	Women with PCOS and CC resistance who attended the infertility clinic. Ovulation induction (N = 280) Inclusion criteria: Clomiphene citrate‐resistant obese women with PCOS diagnosed on the basis of the revised Rotterdam 2003 criteria. The presence of 2 out of 3 criteria (oligo and/or anovulation, clinical and/or biochemical signs of hyperandrogenism, and polycystic ovary) was recommended as diagnostic of PCOS. CC resistance was defined as failure to achieve adequate follicular maturation after 3 consecutive induction cycles with CC at 150 mg/d for 5 days Exclusion criteria: Smokers, drug users, those with other causes of infertility such as a male factor or tubal factor, and those with endocrine disorders such as thyroid dysfunction and hyperprolactinaemia
Interventions	1. CC plus metformin and L‐carnitine: 150 mg/d CC from day 3 to day 7 of menstrual cycle plus oral L‐carnitine (3 g) and metformin 850 mg (1 tablet daily), then the dose was doubled after 1 week to 1700 mg/d (2 tablets daily). Mean age 25.7 years ± 1.7 (N = 140) 2. CC plus metformin and placebo: 150 mg/d CC from day 3 to day 7 of menstrual cycle plus placebo and metformin 850 mg (1 tablet daily), then the dose was doubled after 1 week to 1700 mg/d (2 tablets daily). Mean age 26.1 ± 2.2 (N = 140) Treatment for 3 months
Outcomes	Clinical pregnancy Hormonal level and metabolic profile changes Ovulation First trimester (13 weeks) miscarriage rates
Notes	Location: Department of Obstetrics and Gynecology Faculty of Medicine, Zagazig University, Egypt Timeframe: between January 2017 and March 2018 Trial registration number: not provided Informed consent: yes Ethical approval: yes Sample size power calculation:yes Funding: unknown Conflict of interests: the authors have no conflict of interest to disclose ITT: no Author email: IbrahimSharkwy@yahoo.com The paper states that "This trial has some limitations, the side effects of the medications were not evaluated, we did not include non‐PCOS obese women as a control group, and the live birth rate was not considered" (page 704). Miscarriage rates were reported
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomization was created by the computer" (page 702)
Allocation concealment (selection bias)	Low risk	Quote: "The Allocation was concealed in opaque, sealed, and serially numbered envelopes" (page 702)
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "All women, treating physicians, and investigators were blinded to treatment allocation" (page 702)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcome group: Quote: "The consenting 280 women were randomly allocated to group 1 (N = 140) or group 2 (N = 140). Six women were excluded from analysis due to loss of follow up: two women in group 1 and four women in group 2" (page 702) All dropout numbers explained and accounted for. ITT not used
Selective reporting (reporting bias)	Unclear risk	Clinical pregnancy and miscarriage are reported. Live birth and side effects of medication are not reported. Trial registration number is not available
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Randomised single‐centre controlled clinical trial
Participants	Women undergoing IVF with sleep disturbances (N = 63) from 24 ‐ 38 years Inclusion criteria: unexplained infertility, no ovulatory problems, normal hysterosalpingogram or laparoscopy and normal semen sample Exclusion criteria: chronic drug usage, history of > 1 fertilisation failure, hypertension, diabetes, uterine myoma, ovarian cyst and smoking
Interventions	1. Melatonin 3 mg; 1 tablet a day, taken at 22:00 to 23:00 from 3rd to 5th day of the menstrual cycle until the hCG injection (N = 30) 2. No treatment (N = 30)
Outcomes	Primary outcome: oocyte quality Secondary outcomes: fertilisation failure rate, number of follicles, number of oocytes retrieved, number of Mll oocytes, fertilisation rate, number of embryos transferred, embryo quality, implantation rate and clinical pregnancy rate
Notes	Trial held in Turkey Ethics approved, written informed consent gained. Authors declare no conflicts of interest Power calculation performed Emailed author 9th August 2012 regarding which group or groups lost the 3 women. Data added. Tried to contact the author again regarding live birth data 5th February 2013. Author replied on 7th February 2013, saying that the 3 dropouts were from the treatment group, and that no allocation concealment was performed and no live birth data were available because participants were mainly from rural sites
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were randomly assigned according to a randomisation table
Allocation concealment (selection bias)	High risk	No allocation concealment
Blinding (performance bias and detection bias) All outcomes	High risk	No blinding as control is no treatment
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropouts explained
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. Clinical pregnancy reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Double‐blind randomised trial
Participants	Women with oligomenorrhoea or amenorrhoea and PCOS were recruited from gynaecology, endocrine and fertility clinics. Women were < 35 years of age, mean age 29.7 (N = 92) "Infertility was an ailment in only half of the patients in each group. There was no difference in the proportions of infertile women with the groups". Exclsion criteria: hyperprolactinaemia, hormone treatment, abnormal thyroid function, congenital adrenal hyperplasia
Interventions	1. Infolic^Ⓡ, a combination of myo‐inositol 2g plus folic acid 400 μg: 1 tablet twice a day (N = 45). Mean age 29.0 2. Folic acid 400 μg: 1 tablet twice a day (N = 47). Mean age 29.7 Duration: 16 weeks
Outcomes	Ovulation frequency Hormonal levels Pregnancy
Notes	"Ethical committee approval was obtained before the study, and written informed consent was given by each patient". Trial carried out in Italy, study dates not reported Power calculation carried out High dropouts, > 30% in the treatment group. Included, but data not used, as half the participants did not want to conceive. Study is included on the basis that half the participants were from a subfertility clinic Funding source not reported Authors contacted (May 2010) to request any pregnancy outcomes considered and to ask whether the authors of the paper have the individual data on which women in each group were infertile. No reply as of 12th June 2013
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomisation was effected in a double blind fashion; patients received either MYO combined with folic acid (Inofolic^®) or only folic acid as placebo, according to the code provided by computer‐generated randomization."
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Described as "double‐blind fashion" ("placebo control" however control is folic acid so considered to be no treatment)
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "The high dropout rate in the myo‐inositol arm (more than 30%) is notable".
Selective reporting (reporting bias)	High risk	Only half the participants declared before the study that they wanted to conceive. No ITT for the pregnancy outcome. 1 miscarriage was reported but no details of whether this occurred in the treatment or the control group. Miscarriage not prespecified as an outcome of interest. Trial registration number not available
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Parallel blinded randomised controlled clinical trial
Participants	Women attending an infertility clinic for timed intercourse. The participants were required to have scheduled coitus 24 to 36 hours after the hCG injection. (Mean age 28.6 ± 6.5) (N = 66) Inclusion criteria: (1) age of > 18 years, (2) openness of at least 1 of the uterine tubes based on hysterosalpingogram imaging, (3) lack of endocrine diseases (e.g. hyperprolactinaemia, hypothyroidism, and Cushing’s syndrome), (4) normal semen analysis (spermogram) of the partner, and (5) confirmation of infertility due to PCOS based on the Rotterdam criteria by having at least 2 of 3 criteria, including oligomenorrhea or amenorrhea, clinical or laboratory hyperandrogenism, and detection of polycystic ovary in ultrasound Exclusion criteria: a change in the diagnosis of the disease during the research period and participants’ unwillingness to co‐operate with us in conducting the study
Interventions	1.100 mg of clomiphene (i.e. 2 x 50 mg pills) along with 1200 mg of NAC (i.e. 2 x 600 mg pills, made by Fluid UI MUCIL Co., Iran) (Mean age 28.7 ± 6.9) (N = 33) 2.100 mg of clomiphene (i.e. 2 x 50 mg pills, made by Iran Hormone Co., Iran) (Mean age 28.5 ± 6.2) (N = 33) Taken from the day 3 to day 7 of menstrual cycle
Outcomes	Mean endometrial thickness Mean sizes of the follicles Mean numbers of follicles Positive beta‐hCG result
Notes	Location: Milad Infertility Clinic in Mashhad, Iran Timeframe: In 2015 Trial registration number: IRCT2016042727638N1 Informed consent: Yes Ethical approval: Yes Sample size power calculation: Unknown Funding: Department of Research at Mashhad University of Medical Sciences supported the study Conflict of interests: Authors declare that they have no conflict of interests ITT: Yes Author email: ghomiann@mums.ac.ir Email sent to the author 22 January 2020 concerning; the time period of the trial, clinical data, allocation concealment, blinding, and any dropouts
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “simple random sampling technique” “using a random number table, the patients were divided into two groups of control and intervention” (page186)
Allocation concealment (selection bias)	Unclear risk	Unknown
Blinding (performance bias and detection bias) All outcomes	High risk	Quote: “This blinded randomized controlled clinical trial” Unknown who was blinded (page 186). The control is no treatment
Incomplete outcome data (attrition bias) All outcomes	Low risk	No mention of dropouts. ITT used
Selective reporting (reporting bias)	Unclear risk	Trial registration number available but only biochemical pregnancy reported
Other bias	Low risk	No other bias found

PERMALINK

Antioxidants for female subfertility

Marian G Showell

Rebecca Mackenzie-Proctor

Vanessa Jordan

Roger J Hart

Abstract

Background

Objectives

Search methods

Selection criteria

Data collection and analysis

Main results

Authors' conclusions

Plain language summary

Summary of findings

Background

Description of the condition

Description of the intervention

How the intervention might work

Why it is important to do this review

Objectives

Methods

Criteria for considering studies for this review

Types of studies

Inclusion criteria

Exclusion criteria

Types of participants

Inclusion criteria

Exclusion criteria

Types of interventions

Inclusion criteria

Exclusion criteria

Types of outcome measures

Primary outcomes

Secondary outcomes

Search methods for identification of studies

Electronic searches

Searching other resources

Data collection and analysis

Selection of studies

Data extraction and management

Assessment of risk of bias in included studies

Measures of treatment effect

Unit of analysis issues

Dealing with missing data

Assessment of heterogeneity

Assessment of reporting biases

Data synthesis

Subgroup analysis and investigation of heterogeneity

Sensitivity analysis

Overall quality of the body of evidence: 'Summary of findings' tables

Results

Description of studies

Results of the search

2013 version of the review

2017 Update

1.

Included studies

1. Gerli 2007‐ data not included in meta‐analysis.

Participants

Interventions

Outcomes

Live birth

Clinical pregnancy

2. 'Biochemical' and 'pregnancy' data for those trials that did not specifically report 'clinical pregnancy'.

Design

Funding

Excluded studies

Ongoing trials

Risk of bias in included studies

2.

3.

Allocation

Blinding

Incomplete outcome data

Selective reporting

4.

Other potential sources of bias

Reasons for studies with data included within the review but not in the analysis

*Study characteristics*
Methods	Prospective, randomised, placebo‐controlled, group comparative, double‐blind study
Participants	Subfertile women having 1st IVF cycle aged < 40 years with mean age of 31.73 ± 4.4 years (N = 620) 10% described as male factor infertility, and associated data were not presented separately Inclusion criteria: tubal, idiopathic and male infertility were included Exclusion criteria: women with repeated IVF cycles and women with renal or gastrointestinal disease
Interventions	1. Ascorbic acid 1 g: 1 tablet a day (N = 172) 2. Ascorbic acid 5 g: 1 tablet a day (N = 153) 3. Ascorbic acid 10 g: 1 tablet a day (N = 136) 4. Placebo (N = 158) Duration 1 cycle
Outcomes	Clinical pregnancy rate confirmed by fetal heartbeat at 8 weeks Implantation rate per embryo transfer
Notes	1 woman lost to follow‐up－no explanation. Tried to contact author. No reply 10% of women had partners with male infertility Trial conducted in 2 clinics in Budapest, Hungary (N = 237) and Vienna, Austria (N = 383) No power calculation performed Pregnancies were confirmed at 8 weeks with no further follow‐up; authors contacted regarding this. No reply as of 12th June 2013 No clarity regarding the number of treatment cycles involved in this study Ethics approval not gained as "a study on vitamin supplementation is not subject to IRB approval". Consent forms were signed.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "This prospective randomised double‐blind study". Method not described
Allocation concealment (selection bias)	Low risk	By an independent pharmacy in Vienna "prepared and coded by number".
Blinding (performance bias and detection bias) All outcomes	Low risk	Women and clinicians were blinded: "double‐blind study".
Incomplete outcome data (attrition bias) All outcomes	Low risk	1 set of participant data noted as missing but not explained; authors contacted regarding this
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. Clinical outcomes reported
Other bias	Unclear risk	Unequal baseline group numbers

*Study characteristics*
Methods	Placebo‐controlled double‐blind randomised clinical trial
Participants	Infertile women attending an Obstetrics and Gynaecology clinic. Women with PCOS undergoing timed intercourse (Mean age = ?) (N = 200) Inclusion criteria: PCOS infertile women Exclusion criteria: Unknown
Interventions	1. Clomiphene citrate 100 mg/day plus NAC 1.2 g/day (N = ?)) 2. Clomiphene citrate 100 mg/day plus placebo (N = ?) Treatment for 5 days starting at day 3 of the cycle
Outcomes	The number of follicles > 18 mm on the day of hCG administration Ovulation rates The mean endometrial thickness Pregnancy No adverse side‐effects and no cases of OHSS were observed in the group receiving NAC
Notes	Conference abstract Location: Obstetrics and Gynaecology, El Hussein University Hospital, Cairo, Egypt Timeframe: Unkown Trial registration number: Unkown Informed consent: Unkown Ethical approval: Unkown Sample size power calculation: Unkown Funding: Unkown Conflict of interests:Unkown ITT: Unkown Author email: Unkown and unable to find
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Randomly divided"
Allocation concealment (selection bias)	Unclear risk	Unknown
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Placebo‐controlled double‐blind"
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unknown
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available
Other bias	Unclear risk	Conference abstract ‐ baseline characteristics unclear

*Study characteristics*
Methods	Randomised, double‐blinded, placebo‐controlled trial ‐ parallel
Participants	Women with PCOS attending infertility clinic IVF (N = 40) Inclusion criteria: Women with PCOS, age 18 to 40 years, who were candidate for IVF without prior IVF, were randomly enrolled in this investigation. To confirm PCOS diagnosis, Rotterdam criteria were used Exclusion criteria: Women with metabolic abnormalities such as diabetes, impaired glucose tolerance, and thyroid dysfunction
Interventions	1. 200 μg/day selenium as selenium yeast (Nature Made, California, USA) (Mean age 32.1 ± 4.7) (N = 20) 2. Placebo (Mean age 32.6 ± 3.5) (N = 20) Treatment for 8 weeks
Outcomes	TNF‐α gene expression Gene expression associated with inflammation Endometrial thickness Number of oocytes retrieved Number of fertilised oocytes Fertilisation rate Pregnancy rate Number of embryos
Notes	Location: Mahdieh Hospital, Tehran, Iran Timeframe: between February and August 2018 Trial registration number: IRCT20170513033941N23 Informed consent: yes Ethical approval: yes "Compliance with Ethical Standards" Sample size power calculation: no "Due to a lack of evidence about the appropriate dosage of selenium for infertile patients with PCOS candidate for IVF, we used the above mentioned dose of selenium based on a previous study in patients with PCOS" Funding: This study was supported by a grant from the Vice chancellor for Research, Shahid Beheshti University of Medical Sciences, Tehran, Iran Conflict of interests: "The authors declare that they have no conflict of interest" ITT: no Author email: asemi_r@yahoo.com Emailed author 22 January 2020 asking if women had undergone IVF during the trial, definition of pregnancy data, any live birth data or adverse event data and methods of allocation concealment Dr Asemi replied 23 January 2020 saying yes, women were undergoing IVF at the time of the trial. Emailed Dr Asemi 23 January 2020 asking for clarification on allocation concealment and clinical pregnancy.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "To randomize enrolled patients, computer‐generated random numbers were used"
Allocation concealment (selection bias)	Unclear risk	Quote: "Allocation and randomization were concealed from both the participants and researchers until final analyses completion"
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: “double‐blinded, placebo‐controlled trial” Quote: “Placebos and selenium supplements were exactly matched in terms of appearance, smell, shape, and packaging”
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropouts explained Quote: "Two dropouts were reported in each intervention group, due to personal reasons"
Selective reporting (reporting bias)	Low risk	Trial registration number available, clinical outcomes reported only in the Results section
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Randomised double‐blind, placebo‐controlled, parallel‐group study
Participants	Infertile women with clomiphene resistant PCOS. Mean age: Treatment group: 24.6 ± 3.2; Control group: 24.8 ± 2.7.Ovulation induction with timed intercourse (N = 170) Inclusion criteria; < 35 years of age, presenting with primary or secondary infertility following regular intercourse for at least 1 year and diagnosed with PCOS with no other abnormalities Exclusion criteria; FSH values ≥ 10IU/ml
Interventions	1. Clomiphene citrate 250 mg: 1 tablet a day from day 3 to day 7 of the cycle plus oral‐carnitine 3 g: 1 tablet a day from day 3 until the day of the first positive pregnancy test (N = 85) 2. Clomiphene citrate 250 mg: 1 tablet a day plus placebo (N = 85) All participants received clomiphene citrate from day 3 until day 7 of the cycle.Timed intercourse
Outcomes	Clinical pregnancy rate Miscarriage Multiple pregnancies Ovulation rate Days until hCG injection Endometrial thickness Number of follicles Number of pregnancies Laboratory parameters
Notes	All participants were counselled about their participation in the study. A signed informed consent was obtained. Participants had the right to refuse to participate or to withdraw from the study at any time without being denied their regular full clinical care. Personal information and medical data collected were subject to confidentiality and were not made available to a third party. Women’s Health Hospital, Assiut University, Assiut, Egypt The study was conducted between January 2010 and March 2012 Sample size calculation done "The authors have no conflict to disclose" Funding source not reported Email: 'prof.alaaismail@aun.edu.eg' and 'alaaeldeen.mahmoud@med.au.edu.eg' Email sent to author on 26th November 2015 regarding live birth data; author replied on 7th December 2015 saying there are no live birth data 17 October 2019 we added sub‐study; Salem 2012, there is some discrepancy between the doses of clomiphene in the two papers ‐ the conference abstract Salem states that group A had 100mg clomiphene while Group b had 150mg and pregnancy data is different but this is probably due to early publication of the conference abstract.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "computer‐generated numbers" Quote: "randomized according to computer‐generated randomization tables to ensure an equal number of patients in each arm (1:1 ratio)".
Allocation concealment (selection bias)	Low risk	Quote: "using previously prepared sealed envelopes with computer‐generated numbers" Quote: "Throughout the trial, access to the randomization code was available only to the pharmacist who manufactured the placebo and packed the envelopes and was not available to any of the treating physicians or patients". Quote: "The capsules were placed in sacks and then stored in envelopes numbered from 1 to 170. The envelopes were numbered"
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "double blind" Quote: "The placebo capsules were specially manufactured to look identical to the L‐carnitine capsules".
Incomplete outcome data (attrition bias) All outcomes	Low risk	18/170 dropouts with numbers per group and reasons given
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. All outcomes stated in the Methods were reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Double‐blinded, randomised, clinical trial – parallel
Participants	Infertile women with diminished ovarian reserve who were referred to the infertility center. IVF (N = 80) Inclusion criteria: Poor ovarian reserve ART for the first time, normal male factor, normal uterine cavity, and presence of 2 of the following 3 criteria: 1) summation of bilateral AFC ≤ 6, 2) AMH ≤ 1, and 3) basal FSH on the 3rd day of menstrual cycle ≥ 10. These cases are routinely candidated for egg donation in our centre. Couples who insisted on having the ART by using their own oocytes were enrolled in this project Exclusion criteria: unknown
Interventions	1. Melatonin 3 mg 1 capsule every night starting from the 5th day of the menstrual cycle prior to the cycle that was planned for gonadotropin stimulation (Mean age 35 ± 5.1) (N = 40) 2. Placebo (Mean age 35.1 ± 5.1) (N = 40)
Outcomes	Stimulation duration Estradiol on HCG injection Human menopausal gonadotropin dose Oocytes in germinal vesicle stage Oocytes in maturation stage I (MI) Oocytes in maturation stage II (MII No. of embryos transferred Embryos in grade 1 Embryos in grade 2 Embryos in grade 3 Embryos in grade 4 Women who had mature oocytes (MII) Women who had grade‐1 embryos Women who had top‐quality embryos Women whose embryos were transferred Biochemical pregnancy Clinical pregnancy Miscarriage
Notes	Location: Infertility Center, Mother and Child Hospital, affiliated to Shiraz University of Medical Sciences, Iran Timeframe: between 2014 and 2015. 12‐month period cbeginning in June 2014 Trial registration number: IRCT2014041417264N1 Informed consent: yes Ethical approval: yes Sample size power calculation: yes Funding: The present article was partly extracted from a thesis written by Sara Sadeghi and was financially supported by Shiraz University of Medical Sciences (grant # 92‐5250) Conflict of interests: "none declared" ITT: no Author email: namavarb@sums.ac.ir
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "randomization table" (page 74)
Allocation concealment (selection bias)	Low risk	Quote: "the pharmaceutics specified every package that contained the placebo or melatonin with a code number from 101 to 200 based on a randomization table. The prepared packages, each containing 50 capsules, were offered to the participants orderly based on their entrance into the project. Accordingly, the patients or the clinicians did not know that which package contained the placebo or melatonin" (page 74)
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Capsules containing 3 mg melatonin (Nature Made Nutritional Products, Mission Hills, USA) and placebos with the same shapes were prepared for the study by the Pharmaceutics Division of Shiraz University of Medical Sciences. To design a double‐blinded, simple randomization" (page 74)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Reasons and numbers from each group given
Selective reporting (reporting bias)	Low risk	Trial registration number and reports clinical pregnancy
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Double‐blinded randomised control trial
Participants	Women aged 18 ‐ 41 with PCOS which was clomiphene‐resistant who attended fertility clinic in Iran (N = 93)
Interventions	1. Oral NAC 1.2 g: 1 tablet a day (N = 53) 2. Vitamin C (?dose) (N = 40)
Outcomes	Oestradiol levels Number of follicles > 18 mm Endometrial thickness
Notes	Conducted in Iran, study began in 2010 (end unknown) Unknown trial duration Funding source not reported Tried to contact author regarding pregnancy data, uneven number in each group. No reply.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Double‐blinded (another antioxidant, not placebo)
Incomplete outcome data (attrition bias) All outcomes	High risk	Uneven number in each group
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Prospective randomised controlled study
Participants	Infertile women with a history of unexplained total fertilisation failure undergoing ICSI (N = 98). Ages not given Inclusion criteria: unknown Exclusion criteria: unknown
Interventions	1. Omega‐3‐polyunsaturated fatty acids (o‐3 PUFAs) 1000 mg: 1 tablet a day (N = unknown) 2. Unknown control (N = unknown)
Outcomes	Total recombinant human (rh)FSH dose and days required Numbers of oocytes retrieved Number of oocytes fertilised Embryo quality Embryo implantation Clinical pregnancy rate
Notes	Conference abstract only Trial held in Korea, study dates not reported Funding source not reported Authors emailed 22nd November 2011regarding risk of bias, pregnancy data per woman, numbers in intervention and control groups and inclusion/exclusion criteria. No reply
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Prospective randomised controlled study"－no explanation given.
Allocation concealment (selection bias)	Unclear risk	Unknown
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unknownn.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unknown
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. Clinical pregnancy reported in methods
Other bias	Unclear risk	Conference abstract ‐ baseline characteristics unclear

*Study characteristics*
Methods	Randomised open‐label, multicentre pilot study
Participants	Infertile women undergoing IVF/ICSI, mean age 34.4 ± 3.4 (N = 100) Exclusion criteria: women with PCOS, with any endocrine or metabolic disease, taking any hormonal treatment, with BMI > 30 kg/m²
Interventions	1. Myo‐inositiol 4000 mg: "into two administrations per day" + folic acid 400 µg: 1 tablet a day (N = 50) 2. Folic acid 400 µg: 1 tablet a day (N = 50) Duration of treatment 3 months, duration of trial 12 months
Outcomes	Length of stimulation Total quantity of gonadotropins required Number of oocytes retrieved Implantation rate Clinical pregnancy
Notes	Center for Reproductive Medicine Research, Clinica Villa Mafalda, Rome, Italy, study held from January 2011 to January 2012 Funding source not reported Registration number NCT01338844 Emailed author 13th February 2013 about randomisation, allocation concealment and live birth data. Professor Lisi replied, clarifying these questions
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Block randomisation in a computer‐generated sequence" is written in the paper and in further correspondence from the author ..."About randomization, a computer software generated 100 numbers from 1 to 10,000, and the numbers were stored in sealed envelopes and opened on the day of preparation and explanation of the stimulation protocol to patients. Patients with odd number were assigned to folic acid, myo‐inositol and rhFSH; patients with even number were assigned to folic acid and rFSH". Unsure whether this may be quasi‐randomised. We sought further information from the author. Author replied, "The envelope outside had 100 numbers in order and opened in that order; numbers outside were different from numbers inside".
Allocation concealment (selection bias)	Low risk	Envelopes were numbered sequentially and were opaque
Blinding (performance bias and detection bias) All outcomes	High risk	Open‐label, although outcome assessors were blinded participants were not
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts
Selective reporting (reporting bias)	Low risk	Trial registration number provided. Clinical pregnancy reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Randomised study
Participants	Women with PCOS (based on Rotterdam criteria, ESHRE/ASRM 2004), the diagnosis of PCOS is determined by the presence of 2 of the following conditions: oligo‐ovulation or anovulation, hyperandrogenism and polycystic ovaries detected by ultrasonography with the presence of 12 or more follicles measuring 2 – 9mm in diameter, and/or at least 1 enlarged ovary (410 cm). None of the participants had history of clomiphene citrate resistance (N = 120) Timed intercourse Mean age was 26 years for all 3 groups Exclusion criteria: women with endocrinological abnormalities such as thyroid dysfunction or abnormal prolactin levels, those with hypothalamic or pituitary dysfunctions evaluated by low gonadotropin level, other causes of infertility such as tubal factor evaluated by HSG or laparoscopy, abnormal uterine cavity evaluated by sonohystrography or hysteroscopy and male factor, evaluated by semen analysis. Women with ovarian cysts and those with allergy to the study medications were also excluded from the study. Women who had received any hormonal medications (except progesterone for withdrawal bleeding) within the last 3 months before the study were also excluded
Interventions	1. Clomiphene citrate 100 mg orally in 2 divided doses a day. No treatment (N = 40) 2. NAC 1200 mg in 2 divided doses a day (in the form of powder inserted in small pockets to be diluted into a standard glass of water from day 3 until day 7 of the menstrual cycle) (N = 40) 3. Metformin 500 mg: 1 tablet 3 times a day (N = 40) Treatment period; from day 3 to day 7 of the menstrual cycle, treatment was repeated in non‐pregnant cases for 3 successive cycles
Outcomes	Clinical pregnancy (defined as the presence of gestational sac containing fetal hearts on ultrasound scan) Occurrence and day of ovulation Endometrial thickness and pattern Number and size of follicles
Notes	Conducted in Egypt Trial period; September 2012 to March 2014. Funding source not reported Ahmed Mohamed Maged, Obstetrics and Gynecology Department, Kasr Aini Hospital Cairo University, 135 King Faisal Street Haram Giza, Cairo, Egypt. Tel: 0105227404. Fax:35873103. E‐mail prof.ahmedmaged@gmail.com. Email sent 13th October 2016 regarding live birth and any dropouts. No reply.
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were randomised at the beginning of each cycle by sealed opaque envelopes containing randomly‐generated numbers into 3 groups
Allocation concealment (selection bias)	Low risk	Participants were randomised at the beginning of each cycle by sealed opaque envelopes containing randomly‐generated numbers into 3 groups
Blinding (performance bias and detection bias) All outcomes	High risk	No blinding
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Numbers analysed in each group are not given
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available. Clinical pregnancy reported
Other bias	Low risk	No other bias found

*Study characteristics*
Methods	Single‐centre, double‐blinded, placebo‐controlled, randomised trial
Participants	Women (age: 22 ‐ 40) with at least 2 repeated implantation failure (RIF) history. IVF (N = 30)
Interventions	1. NAC 1200 mg/day (N = ?) (Mean age = ?) 2. Placebo (N = ?) (Mean age = ?) For at‐least 9 weeks before starting ovarian stimulation
Outcomes	Level of HOXA9 gene
Notes	Conference abstract Location: Research and Clinical Center for Infertility, Shahid Sadoughi University of Medical Sciences, Yazd, Iran Timeframe: Unknown Trial registration number: Unknown Informed consent: Unknown Ethical approval: Unknown Sample size power calculation: Unknown Funding: Unknown Conflict of interests: Unknown ITT: Unknown Author email: Unknown
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Unknown methods
Allocation concealment (selection bias)	Unclear risk	Unknown methods
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "double blinded, placebo controlled"
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unknown
Selective reporting (reporting bias)	Unclear risk	Trial registration number not available and no clinical outcomes
Other bias	Unclear risk	Conference abstract ‐ baseline characteristics unclear