Effect of fennel extract on Anti-Müllerian Hormone and sonographic indices in infertile women with occult premature ovarian insufficiency: a randomized controlled clinical trial

Abstract

Background

Premature Ovarian Insufficiency (POI) is a condition characterized by the inability to ovulate before the age of 40. The occult type of POI (OPOI) is associated with a significant decrease in fertility and normal FSH levels. Fennel (Foeniculum vulgare Mill.) is known for its antioxidant properties and potential benefits on ovarian function. This study aimed to determine the effect of fennel extract on Anti-Müllerian Hormone (AMH) levels and antral follicular count (AFC) in infertile women with occult premature ovarian insufficiency.

Methods

This randomized controlled clinical trial was conducted at Tabriz University of Medical Sciences. 60 Infertile women with OPOI were randomly assigned to either the intervention group, who received fennel extract, or the control group, who received a placebo, with a ratio of 1:1. AMH measurement and AFC were performed at baseline and after 60 days, on the third day of menstruation.

Results

AMH level and AFC at the baseline were not statistically significant between fennel and the placebo groups(p > 0.05). After the intervention, the difference in changes of AMH between the two groups was not statistically significant (p = 0.986). However, AFC in fennel group was significantly higher than the placebo group after intervention (mean difference = 1.6; confidence interval of 95%: from 0.07 to 3.1; p = 0.040).

Conclusion

Fennel extract may have a beneficial effect on AFC in infertile women with occult POI, but had no effect on serum AMH levels. Further studies are needed to reach more definitive results in this field.

Trial registration

This trial has been registered at Iranian Registry of Clinical Trials (IRCT20111219008459N15). Submitted 1 February 2023, registered 5 February 2023 prospectively (https://irct.behdasht.gov.ir/user/trial/67583/view).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-025-05078-4.

Background

Premature Ovarian Insufficiency (POI), also known as hyper gonadotropic hypogonadism, is defined as the inability to ovulate before the age of 40 [1, 2]. POI includes both follicular dysfunction and follicular depletion [3], and is classified into three categories: overt, biological, and occult. The occult type is associated with a significant decrease in fertility and normal FSH levels; in the biological type, the individual experiences irregular periods and increased FSH levels (40 − 10 IU/L); and in the overt type, the individual experiences irregular periods with high FSH levels (> 40 IU/L) [4, 5].

This condition affects 1 in 1000 women under 30 years of age [6]. The overall prevalence of POI is reported to be 3.7%, and it has an inverse relationship with the Human Development Index [7]. The prevalence of POI in Iran is reported to be 3.5% [8].

Clinically, in the short term, POI may lead to failure of breast development or arrested puberty; primary, secondary, or primary- secondary amenorrhea; hot flashes and night sweats; dyspareunia; decreased libido; sleep and mood disorders [9]; neurological dysfunction [10]; and infertility [11]. In the long term, it may lead to bone demineralization and an increased risk of cardiovascular diseases [7] and cognitive and psychomotor impairments [12]. The impact of estrogen deficiency associated with POI on bone mineral density (BMD) is well established. Recent studies show that in 3.4% of women with a normal karyotype and spontaneous POI, compared to healthy individuals, the measured BMD at the femoral neck significantly decreases [13].

Many causes of POI are unknown [14]. They often occur sporadically. However, in 10–15% of cases, they are related to genetic problems [15]; immunity [16]; or anti-ovarian antibodies [17] and may be associated with infertility [18], infections [10], lifestyle [19], environmental toxins, or iatrogenic causes [7].

The recommended treatment for women with POI, considering estrogen deficiency and reduced fertility [20], is the use of donor oocytes in women with overt POI. In this case, these couples do not become biological parents of their children [21].

Antioxidants delay the depletion of ovarian reserves that occurs in POI [22]. Antioxidant pathways originate from triggers that lead to the formation of free radicals (FRS) [23]. FRS, through reactive oxygen species (ROS), cause irreversible cellular damage [24]. Excessive ROS leads to oxidative stress and disrupts female reproduction because granulosa cells (GCs) are sensitive to ROS [25]. By activating pathways such as mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK), it initiates cell death. Abnormal apoptosis and dysfunction of GCs due to oxidative stress (OS) lead to pathological changes in the ovaries, ultimately resulting in POI [26].

Foeniculum vulgare Mill., commonly known as fennel, is a fragrant plant from the Apiaceae family and is typically found in the Mediterranean region [27]. The main components of the essential oil extracted from fennel seeds include Trans-anethole(74%), Fenchone(11%), Estragole(3.5%), Limonene(5.2%), and α-Pinene(2.8%) [28]. F. vulgare is recognized as a rich source of natural antioxidants [29], which react with free radicals and may limit free radical damage in the human body through radical scavenging or cleansing activity [30]. A human study has shown that this plant has a positive effect on ovarian reserves, possibly due to the presence of phytoestrogens such as Isoflavones, Prenylated Flavonoids, and Coumestans. Phytoestrogens have anti-inflammatory properties that can reduce C-reaction protein (CRP) levels. CRP levels are inversely related to fertility, with a decrease in CRP levels increasing fertility [31]. A study on mice showed that fennel extract at concentrations of 100 mg/kg and 200 mg/kg could significantly increase serum levels of estrogen, progesterone, and prolactin in the intervention groups compared to the control group [32]. A study conducted in Iran on Wistar rats aimed to investigate the impact of aqueous extracts of fenugreek root, fennel seeds, and milk on fertility and the sex ratio of offspring. The results indicated that the fennel seed extract significantly enhanced the number of pregnant rats and the total number of newborns when compared to the control group and the other treatment groups [33]. Another study aimed to examine the direct effects of fennel on fundamental ovarian cell functions, including proliferation, apoptosis, and the response to physiological hormonal stimuli like ghrelin. The findings revealed that fennel could shift the balance of apoptosis towards proliferation, potentially stimulating ovarian cells and folliculogenesis [34]. A systematic review and meta-analysis indicated that F. vulgare may be more beneficial than hormone replacement therapy (HRT) for improving menopausal symptoms, including reduced sexual performance, vaginal atrophy, and psychological symptoms. Side effects of F. vulgare, such as rash, frequent urination, nasal congestion, abdominal pain, unlike the long-term risks of HRT, are situational and reversible upon discontinuation of the medication. However, clinical use should be cautious, as existing studies provide limited evidence for the superiority of fennel over HRT in managing menopausal symptoms [35]. Additionally, a systematic review and meta-analysis showed that the consumption of F. vulgare led to a reduction in anxiety and depression scores, symptoms of hot flashes, and improved sleep disturbances in menopausal women. However, F. vulgare did not have a positive effect on bone density, lipid profile, and body mass index in menopausal women [36].

Approximately 15% of couples worldwide have fertility problems, most of which are due to female factors. Conventional treatments such as the use of hormonal drugs or assisted reproductive techniques, due to side effects, less-than-expected treatment response, and high costs, are unaffordable for many couples, leading to a preference for herbal medicines [37].

Measuring the level of Anti-Müllerian Hormone (AMH), which is produced by follicles, is the most reliable test for detecting ovarian reserve dysfunction [7]. Additionally, based on a study conducted on individuals with Occult Premature Ovarian Insufficiency (OPOI), these women with unexplained infertility can be identified with reduced ovarian reserve through the measurement of the antral follicular count (AFC) [38]. Therefore, AMH and AFC are good criteria for screening individuals with infertility and oligo menorrhea due to OPOI [39].

Given the importance of fertility in the stability of family foundations, the high cost and numerous side effects of pharmaceutical treatments, and the limited number of studies on the effect of fennel extract on sex hormone levels in female mice and one quasi-experimental human study in this area, the present study was designed to determine the effect of fennel extract on Anti-Müllerian Hormone levels and sonographic indices in infertile women with occult premature ovarian insufficiency.

Methods

Study design and participants

This study is a randomized controlled clinical trial (participants, intervention performers, outcome assessors, and data analysts were blinded to the type of intervention received) designed to investigate 60 women with occult premature ovarian insufficiency (OPOI) who presented to the Al-Zahra Infertility Clinic of Tabriz University of Medical Sciences in 2023. We adhered to the CONSORT guidelines for the standardized reporting of randomized trials [40]. Inclusion criteria included women aged 20–40 with regular menstrual cycles, evidence of POI (AMH < 1 ng/ml), or reduced ovarian follicular reserve as indicated by transvaginal sonography (fewer than 6 antral follicles in each ovary), presence of both ovaries, and no other causes of infertility based on their medical records, and no use of herbal medications in the past three months. Exclusion criteria included alcohol or tobacco use, obesity (BMI > 30 kg/m²), preference for donor egg use, history of cancer or radiotherapy or chemotherapy, presence of ovarian cysts or uterine myomas, treatment with the antibiotic ciprofloxacin [41], or signs of menopause (hot flashes, night sweats).

Sampling

After approval by the Ethics Committee of Tabriz University of Medical Sciences (ethical code: IR.TBZMED.REC.1401.966) and registration of the title at the Clinical Trials Center (IRCT20111219008459N15), convenience sampling was conducted. At the infertility clinic, patients were identified based on the diagnosis of occult type of premature ovarian insufficiency (OPOI) confirmed by an infertility specialist. Those who did not wish to use donor eggs were fully informed about the nature and objectives of the study. If they consented to participate, a written informed consent form was obtained.

After controlling the inclusion and exclusion criteria, demographic and medical questionnaires were completed by the participants in the presence of the researcher. Blood AMH levels and antral follicle count (AFC) were assessed before and after the intervention. For AMH assessment, 3 ml of blood were drawn from the brachial vein and tested using an ELISA kit by a laboratory technician at Al-Zahra Hospital. AFC was performed on the third day of the menstrual cycle using real-time transvaginal sonography with a Medison v 20 machine made in South Korea by a radiologist at Al-Zahra Hospital for all participants. The number of antral follicles with a diameter of approximately 3–9 mm in each ovary was recorded separately by the researcher on a checklist.

Sample size

The sample size was calculated based on a study by Farhadi et al. [42] using G-power software, considering the mean AFC in women with POI and assuming a 30% increase due to the intervention (M2 = 5.2, M1 = 4.0, SD1 = SD2 = 1.5), with an alpha of 0.05 and a beta of 0.80. The required sample size for each group was 26, and considering a 15% dropout rate, the sample size was calculated as 30 per group. Additionally, considering the AMH level in women with POI from the study by Farhadi et al. [42] (M1 = 0.56), assuming a 50% increase due to the intervention (M2 = 0.84), and SD1 = SD2 = 0.35, with an alpha of 0.05 and a beta of 0.80, the required sample size for each group was calculated as one. Therefore, the current study considered a sample size of 30 participants per group.

Randomization and intervention

Participants were randomly assigned to two groups just before the start of the intervention in a 1:1 allocation ratio using block randomization with blocks of four and six. Randomization was conducted by an individual not involved in the sampling process using the Randomizer software to ensure allocation concealment, and the intervention received (drug or placebo) was placed in sequentially numbered, opaque vials, thus blinding the sampler and outcome assessor. During the intervention period, participants took three 300 mg fennel tablet or a placebo daily. The fennel tablets and their placebos, which were indistinguishable in shape and color, were prepared by Barij Essence Pharmaceutical Company and were administered three times a day for two months (the time required for the growth of pre-antral follicles is approximately two months [43]. Additionally, participants were reminded weekly via telephone calls about the importance of daily medication use, and potential side effects were also assessed.

Statistical analysis

The data were analyzed using descriptive statistics (frequency, percentage, mean, and standard deviation) and inferential statistics with SPSS version 26. Independent t-tests were used to compare the intervention and control groups in terms of quantitative variables such as age, age at menarche, BMI, and FSH levels. The Chi-square test was used to compare educational levels, and Fisher’s exact test was used to compare occupation, type of infertility, and menstrual cycle regularity. The Mann-Whitney U test was used to compare AMH levels and AFC before the intervention due to the non-normal distribution of the variables. After the intervention, ANCOVA was used to compare AMH levels and AFC between the groups, adjusting for baseline values. All analyses were based on the intention-to-treat approach. Side effects were reported using descriptive statistics (frequency and percentage).

Results

A total of 100 women with POI were enrolled in the study from June 2023, to October 2023, and their follow-up ended on January 2024. Twenty-five participants were excluded due to not meeting the inclusion criteria, and 15 declined to participate. Therefore, 60 women were randomly and equally assigned to the fennel and control groups. In the fennel group, two participants dropped out due to headaches and palpitations, and two due to amenorrhea; in the placebo group, two dropped out due to amenorrhea and one due to a headache. Ultimately, 26 participants in the fennel group and 27 in the placebo group were analyzed Fig. 1.The demographic characteristics of the women in the intervention and control groups were shown in Table 1. There were no statistically significant differences between the groups in terms of demographic characteristics except for place of residence(p = 0.032) (Table 1).

Fig. 1.

Flow chart of the study

Table 1.

Socio-demographic characteristics of the participants in study groups

Variable		Fennel (30 = n)	Placebo(30 = n)	P-value
Age (years)**		38/6 ± 1/9	38/1 ± 2/4	0/415†
BMI**		26/9 ± 2/9	26/9 ± 4/3	†0/386
Gravida*				‡0/204
0		20 (66)	22 (74)
1		7 (24)	6 (20)
2 or more		3 (10)	2 (6)
Number of births*
0		24 (80)	24 (80)	‡>0/99
1		(20) 6	6 (20)
Number of living child*
0		24 (80)	24 (80)	‡>0/99
1		6 (20)	6 (20)
Number of abortions*
0		23 (76)	28 (93)	‡0/054
1		5 (17)	2 (7)
2 or more		2 (7)	0 (0/0)
Regular menstruation		29 (97)	30 (100)	§>0/99
Infertility period (years)**		8/7 ± 5/5	7/2 ± 4/7	†0/278
Type of infertility				0/779§
Primary		20 (67)	22 (73)
Secondary		10 (33)	8 (27)
Occupation				>0/99§
Housekeeper		24 (80)	23 (77)
Employed		6 (20)	7 (23)
Education				0/558‡
Illiterate		2 (7)	3 (10)
Elementary		13 (43)	6 (20)
High school		3 (10)	6 (20)
Diploma		5 (17)	10 (33)
University		7 (23)	5 (17)
Income				0/333‡
Enough		29 (96.7)	28 (93.3)
Insufficient		0 (00)	1 (3.3)
Relatively enough		1 (3.3)	1 (3.3)
House Status				0/032††
Personal		10 (33.3)	12 (40.0)
Rental		10 (33.3)	16 (53.3)
Relative’s house		10 (33.3)	2 (6.7)

*Number (%), **mean(SD), ^§Fisher’s exact test, ^†Independent t-test, ^††Chi-square test, ^‡Trend Chi-square test

The Mann-Whitney U test showed that there was no statistically significant difference in AMH levels between the fennel and placebo groups before the intervention (P = 0.0825). After the intervention, according to ANCOVA, there was no statistically significant difference in AMH levels between the intervention and control groups (mean difference = 0.00; confidence interval of 95%: from − 0.29 to 0.29; p = 0.986) (Table 2).

Table 2.

Comparison of Antimullerin hormone and antral follicles before and after the intervention in study groups

	Fennel group(n = 30)		Placebo group(n = 30)
Variable	Median (first and third quarter)	Mean (standard deviation)	Median (first and third quarter)	Mean (standard deviation)	Mean difference (95% confidence interval)	P-value*
AMH
Before intervention	0.24(0.00 to 0.66)	0.35(0.39)	0.13(0.00 to 0.53)	0.32(0.39)		0.825*
After intervention	0.34(0.00 to 0.89)	0.37(0.53)	0.49 (0.00 to 0.76)	0.39(0.46)	0.00(−0.29 to 0.29)	0. †986
AFC
Before intervention	2.5 (1.0 to 4.0)	3.0(2.1)	2.5 (2.0 to 5.0)	3.4(2.4)		0.572*
After intervention	4.0 (1.0 to 7.0)	3.4(3.1)	2.0(1.0 to 5.0)	2.8(2.4)	1.6(0.07 to 3.1)	0.040†

AMH antimullerian hormone, AFC antral follicular count

†ANOVA test with control of base score and residence variable, * U-Mann-Whitney test

The Mann-Whitney U test indicated that there was no statistically significant difference in AFC between the fennel and placebo groups before the intervention (P = 0.572). However, after the intervention, based on ANCOVA and controlling for baseline scores and place of residence, there was a statistically significant difference in AFC between the intervention and control groups (mean difference = 1.6; confidence interval of 95%: from 0.07 to 3.1; p = 0.040) (Table 2).

Side effects of the supplement were assessed as a secondary outcome. There were one case of abdominal pain and one case of palpitations in the fennel group, and one case of headache in the placebo group.

Discussion

The results of this randomized clinical trial showed that fennel increased ovarian reserve, as evidenced by a significant increase in AFC in the intervention group compared to the control group after the intervention period. However, there was no significant increase in AMH levels in the intervention group compared to the control group.

Phytoestrogens are polyphenolic compounds that can be divided into two groups: flavonoids and isoflavonoids. Isoflavonoids have a structural and functional similarity to mammalian estrogens, particularly 17β-estradiol [44]. Isoflavones have anti-inflammatory properties that may reduce C-Reactive Protein (CRP) levels [45]. CRP has an inverse relationship with fertility, and its reduction can increase fertility [46]. Additionally, isoflavonids have anti-cancer and antioxidant properties. In individuals with POI, increased reactive oxygen species(ROS) levels lead to impaired folliculogenesis and increased apoptosis of primordial cells. Studies have shown that in animals receiving antioxidant supplementation, the number of normal eggs increased compared to the control group, and the percentage of apoptotic eggs decreased [47]. Therefore, it can be said that fennel, with its phytoestrogenic compounds and antioxidant properties, can help in individuals with premature ovarian Insufficiency.

A study by Fallah Hosseini and Kianbakht in Iran in 2012 on Wistar rats aimed to determine the effects of aqueous extracts of fenugreek root, fennel seeds, and milk on fertility and the sex of newborn rats. The study showed that the number of pregnant rats and the total number of newborns in the fennel group significantly increased compared to the control and other groups (P < 0.01), but there was no significant difference in the number of male and female newborns in the fennel group, the number of pregnant rats, and the total number of male and female rats in the fenugreek and milk groups compared to the control group (P > 0.05). Fennel, due to its phytoestrogen content, may stimulate ovulation and increase fertility through mechanisms similar to human chorionic gonadotropin (HCG) and human menopausal gonadotropins (HMG), and thus may be effective in treating infertility [48].

Another study by Sirotkin et al. in 2020 aimed to investigate the direct effects of fennel on the basic functions of ovarian cells, such as proliferation, apoptosis, and response to physiological hormonal stimuli, such as ghrelin. The study showed that fennel could change the apoptosis ratio in favor of proliferation, thereby potentially stimulating ovarian cells and folliculogenesis [49].

In a study by Yavangi et al. in 2020 to determine the effect of fennel extract on fertility outcomes in assisted reproductive technology (ART) in women with poor ovarian response, 41 infertile women with POF were assessed. Before and after treatment with fennel extract, levels of LH and FSH, ovarian volume, and the number of antral follicles were measured on the third day of the menstrual cycle and mid-cycle. Patients consumed 50 cc of fennel extract nightly and after two months of treatment with fennel, laboratory tests and sonography were repeated; then, an ovarian stimulation protocol was used. Significant differences in serum LH levels (P = 0.002), the LH/FSH ratio (P = 0.049), the number of ovarian follicles (P = 0.003), the number of oocytes (P = 0.003), and ovarian volume (P = 0.03) were observed two months after treatment with fennel based on the results of the Wilcoxon test. However, there was no significant difference in the number of embryos after the intervention (P = 0.677); but the results showed a significant difference in ovarian thickness after the intervention (P = 0.04). This study indicates that fennel plays an effective role in improving fertility indicators [31].

Pre-ovulatory follicles have antioxidant properties; for example, glutathione, a water-soluble antioxidant synthesized intracellularly [50], keeps the level of peroxidases low within the follicles [51]. Reactive oxygen species (ROS) in normal amounts are considered important signaling molecules in physiological functions. In relation to ovarian function, ROS in normal amounts play a crucial role in the maturation of oocyte meiosis [26]. Excessive ROS exceed the capacity of antioxidants to neutralize them [52],leading to oxidative stress, which through DNA damage and reduced DNA oxidation and repair in granulosa cells, and reduced nutrient and survival factor transfer to the oocyte, leads to apoptosis [23]. Thus, oxidative stress has harmful effects on follicles and oocytes, limiting the maturation of follicles and oocytes and reducing their quantity and quality [25], disrupting folliculogenesis and increasing apoptosis of primordial follicle cells [53]. These pathological changes in the ovary may ultimately lead to premature ovarian insufficiency (POI) [26].

Antioxidants from exogenous sources are able to counteract the undesirable effects of OS on the ovary and show good therapeutic effects in preventing and treating POI [23]. In a study by Zhengjie et al. to determine the effect of the antioxidant curcumin on 60 female mice that had developed POI due to D-galactose, the level of AMH in the group receiving curcumin plus D-galactose was higher, and apoptosis of granulosa cells and markers of oxidative stress were lower compared to the control group and the group receiving galactose alone. Additionally, the number of antral follicles increased in the curcumin-receiving group [54]. This research shows that antioxidants have a positive effect on the revival of ovaries after damage due to oxidative stress.

In another study by Hongxia Xu et al., the antioxidant effects of melatonin on ovarian reserve capacity, granulosa cells, AMH, and FSH in female mice that had developed POI due to Cyclophosphamide (CTX) were investigated. The study found that melatonin treatment significantly reduced serum levels of FSH and LH (p < 0.05) and increased serum levels of E2 and AMH (p < 0.01). This study also showed that melatonin, as an antioxidant, preserved the hormonal status of the ovary, increased ovarian indices, enhanced follicular growth, and inhibited granulosa cell apoptosis in a mouse model of POF induced by CTX [55].

In a similar study by Moradi et al., the antioxidant effects of 0.5 mg/kg/day Capsaicin (CAP) and 100 mg/kg/day Quercetin (QUR) on POF caused by cyclophosphamide (CYC) in a mouse model were examined. In this study, ovarian volume decreased in mice with POF, and apoptosis of ovarian cells increased as a result of CYC injection. After treatment with CAP and QUR, ovarian volume significantly increased with a reduction in the expression of pro-apoptotic genes, and serum AMH levels and the number of follicles significantly increased. This study showed that CAP could improve tissue markers of oxidative stress [56].

Overall, the results of these studies indicate that antioxidants have a positive effect on increasing ovarian reserve, particularly AMH levels.

F. vulgare has antioxidant activity and is used to protect against damage from oxidative stress [29]. In a study by Ağaçayak et al. in Turkey to determine the causes and treatment of premature ovarian insufficiency in women who visited the Obstetrics and Gynecology Clinic of the Faculty of Medicine at Dicle University between 2012 and 2014, a total of 30 women aged 18 to 40 who were diagnosed with POI based on clinical and laboratory signs and 30 healthy individuals matched for ethnicity and age were included in the study. Blood glucose levels, lipid profiles, and sex hormones (FSH, LH, E2), TSH, PLT, and oxidative stress indices (TOS, OSI) were examined in participants between days three to five of the menstrual cycle. Based on laboratory results, there were no significant differences between the groups in terms of lipid profiles, prolactin, TSH, and glucose levels. However, OSI, TOS, LH, and FSH levels were higher in POI patients compared to controls. Based on this study, it is recommended to use antioxidants for the treatment of infertile women with POI [57].

A study by Fahimeh Pourjafari and colleagues aimed to investigate the effects of two well-known medicinal plants (fennel and flaxseed) on serum AMH levels and AMH expression in the ovaries of first-generation female mice. In the fennel group, AMH + cells increased in all follicles regardless of size, intensity, and age. AMH expression in the fennel and fennel plus flaxseed groups significantly increased compared to the control and flaxseed groups (P = 0.05). The number of antral follicles in the fennel and fennel plus flaxseed groups significantly increased compared to the flaxseed group (P = 0.02 and P = 0.03, respectively) [45].

In contrast, in a human study by Shuyu Wang and colleagues in China aimed to determine the antioxidant effect of Coenzyme Q10 on ovarian response and embryo quality in young women with low basal levels and reduced ovarian reserve. The study showed that baseline FSH levels on the third day of the menstrual cycle were significantly lower after 60 days of CoQ10 supplementation compared to pre-treatment levels in the same group of women. In contrast, AMH and AFC levels before and after CoQ10 treatment were almost the same. The amount of gonadotropin used in the CoQ10 treatment group was significantly lower than in the control group (P = 0.03). The duration of gonadotropin treatment in participants under CoQ10 treatment was shorter, but this difference was not statistically significant (P = 0.08). The peak serum E2 concentration in the CoQ10 group was significantly higher, but there was no difference in the mean endometrial thickness on the day of hCG start between the two groups. In the CoQ10 treatment group, there were fewer IVF cycle cancellations due to optimal ovarian response (5.23%, 4.76) compared to the control group (10.75%, 10.93), although this difference did not reach statistical significance (P = 0.27). The average number of retrieved oocytes after pre-treatment with CoQ10 was significantly higher than in the control group (P = 0.002). The mean number of fertilized oocytes and the fertilization rate in women treated with CoQ10 were significantly higher than in the control group (P < 0.05) [58]. In this study, the duration of treatment was similar to ours and indicates that antioxidant treatment for 60 days can increase the number of oocytes but may not affect AMH levels. Perhaps longer follow-up and longer intervention periods could yield better results.

Limitations and strengths

The strengths of this study are the complete observance of clinical trial principles, including random allocation and blinding; conducting follow-up phone calls with participants to ensure regular use of drug/placebo. Limitations of this study included not measuring other hormones involved in premature ovarian insufficiency such as FSH and estrogen, as well as a small number of research participants due to financial constraints, which hindered the generalization of the study to all individuals affected by hidden premature ovarian insufficiency. Conducting studies with a larger sample size and longer follow-up time, as well as measuring other hormones involved in premature ovarian failure, dominant follicles and the number of pregnancies, is recommended.

Conclusion

Fennel extract may have a beneficial effect on AFC in infertile women with occult POI, but had no effect on serum AMH levels. It seems that more studies with larger sample sizes are needed to confirm or refute the results of this study to speak with greater certainty about the effectiveness of this intervention and to use them as effective, inexpensive, safe, and acceptable interventions for patients to manage premature ovarian insufficiency in the future.

Abbreviations

POI

Premature Ovarian Insufficiency

OPOI

Occult Premature Ovarian Insufficiency

AMH

Anti-Müllerian Hormone

AFC

Antral Follicular Count

OS

Oxidative Stress

OSI

Oxidative Stress Indices

Authors’ contributions

MB, SHH, SMA, RI, and LF contributed to the study design. MB, ESH, VR and EE performed the study. MB, SHH, and SMA contributed to data acquisition and data analysis. SMA, RI and SHH interpreted and discussed the data and critically revised the manuscript. All authors read and approved the final manuscript.

Funding

The project was financed by Tabriz University of Medical Sciences (Grant No. 70757). The funding was spent on sampling and conducting the study.

Data availability

Data and materials of this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the Helsinki Declaration and relevant guidelines. All participants were given the necessary information about the study and their informed written consent was obtained. The Ethics Committee of Tabriz University of Medical Sciences confirmed the study (ethical code: IR.TBZMED.REC.1401.966).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.