Effect of SARS-CoV-2 infection on pregnant outcomes after embryo transfer: a multicenter retrospective study

Abstract

Research question

With the nationwide relaxation of controls for the COVID-19 epidemic from December 2022 in China, fertility and in vitro fertilization (IVF) centers reported increasing numbers of infected patients in a short time. However, there is a lack of information regarding the effects of SARS-CoV-2 infection on pregnancy outcomes after IVF–embryo transfer (ET)/intracytoplasmic sperm injection (ICSI)–ET/frozen–thawed embryo transfer (FET), especially the live birth rate.

Design

This multicenter retrospective study was conducted at three public IVF centers in Jiangsu province of China. Women aged 20–42 years who were undergoing IVF–ET/ICSI–ET/FET treatment were consecutively registered from November 23, 2022 to January 7, 2023, with follow-up until October, 2023. Patients during the same period in the previous year were included in the control group. Each woman contributed only one transplantation cycle. Multivariate regression analysis was used to evaluate clinical outcomes primarily between different policy period other than individual infected or not. Covariates included demographic characteristics (age, body mass index (BMI), infertility cause, anti-müllerian hormone (AMH), and Antral Follicle Counting(AFC)) as well as cycle characteristics (treatment protocol, endometrial thickness, number of embryos transferred, and embryonic morphology).

Results

In this study, we included 779 women in the FET group and 168 women in the IVF–ET/ICSI–ET group, analyze the clinical outcomes of each group separately before and after the relaxation of controls for the COVID-19 epidemic. Pregnancy outcomes, including the clinical pregnancy rate, miscarriage rate, ongoing pregnancy rate, multiple pregnancy rate, and live birth rate, did not change significantly in different policy period. However, the rate of gestational diabetes mellitus (GDM) in FET cycles rather than IVF–ET/ICSI–ET cycles after the relaxation of controls was higher than that 1 year earlier (17.8% vs. 6.8%).

Conclusions

The findings of this study suggest that the relaxation of controls for the COVID-19 epidemic does not have a clear negative effect on the pregnancy outcomes after ET, despite current clinical concerns. Nevertheless, the morbidity of gestational diabetes in FET cycles after the relaxation of controls warrants greater attention.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-026-08945-1.

Background

In 2020, the World Health Organization named the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease coronavirus disease 2019(COVID-19) and declared it a pandemic. From 2019 to 2022, China has taken various measures to avoid spread of the virus. During that period, the couples who infected with SARS-CoV-2 were quarantined strictly and impossible to undergo in vitro fertilization–embryo transfer (IVF–ET) treatment in the reproductive medicine department. On December 7, 2022, the Joint Prevention and Control Mechanism Comprehensive Group of The State Council of China issued the Notice on Further Optimizing and Implementing the Prevention and Control Measures of the Novel Coronavirus to minimize the impact of the epidemic on people’s work and daily life, as well as economic and social development. Controls for the epidemic were relaxed, and the Chinese people entered a peak period of infection. After the time that epidemic controls were relaxed, 80% of infertile couples who underwent IVF–ET developed COVID-19 infection. However, it remains unknown whether the relaxation of controls affects the outcomes of IVF pregnancies.

It has been shown that in women infected with SARS-CoV-2 who have received assisted reproductive technology (ART) treatment, viral RNA is undetectable in the follicular fluid, oocytes, cumulus cells, and endometrium [1–4]. But the co-expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) were detected in nonhuman primate ovarian tissue, and not observed in ovarian somatic cells, which made oocytes to have the receptor/protease machinery to be more susceptible to SARS-CoV-2 infection [5]. Another study demonstrated that SARS-CoV-2 immunoglobulin G could be detected in follicular fluid from both infected and vaccinated patients who have undergone IVF, but there was no evidence of compromised follicular function [6].

Some studies have confirmed that SARS-CoV-2 can gain access to the testes, prostate tissue and semen [7–10], with a significant impact of COVID-19 infection on multiple aspects of semen quality (percentage of total motility, percentage of progressive motility, and normal sperm morphology) [11–15]. DNA damage to sperm may also influence the health and well-being of offspring [16].

One study conducted in two large IVF units in Israel between October 2020 and June 2021 reported that SARS-CoV-2 infection did not affect fresh ART treatment outcomes [17]. Another study in Italy at the beginning of 2020 showed no differences in the rate of spontaneous miscarriage in an ART group before and after the start of the COVID-19 pandemic [18]. A retrospective study with a small sample size in China reported no differences in terms of the biochemical pregnancy rate, clinical pregnancy rate, early miscarriage rate, or implantation rate after ART treatment from May 2020 to February 2021 [19].

On 5 May, 2023, the World Health Organization declared that COVID-19 was no longer a public health emergency of international concern, but that SARS-CoV-2 could remain present for a long period, with seasonal epidemic characteristics similar to influenza virus. As reported in a systematic review including 108 pregnant women with COVID-19 infection, 68% and 34% of women presented fever and coughing in the third trimester, respectively, 59% presented lymphocytopenia, and 70% of women had elevated C-reactive protein [20]. Pregnant women are more vulnerable to severe infection owing to physiological changes that occur during pregnancy. Compared with pneumonia in nonpregnant women, pneumonia during pregnancy has increased morbidity and mortality [21]. Therefore, real-world data are needed to explore the long-term impact of SARS-CoV-2 infection on humans, especially with infection during pregnancy. The infected population in China grew rapidly after relaxation of control policies in China owing to the high infectivity of SARS-CoV-2. The impact of COVID-19 on the health of offspring remains a topic of ongoing exploration and research.

In the present study, we aimed to evaluate the effect of variations in epidemic control policies on the outcomes of IVF–ET, intracytoplasmic sperm injection (ICSI)–ET, or frozen–thawed embryo transfer (FET).

Methods

This was a multi-center retrospective cohort study conducted among all consecutive patients attending our three IVF clinics for various causes of infertility who underwent IVF–ET/ICSI–ET/FET treatment between November 23, 2022 to January 7, 2023. Exclusion criteria were: severe organ dysfunction, active infectious diseases, untreated malignancies, recent exposure to teratogens, severe genetic disorders, uterine abnormalities preventing pregnancy, substance abuse, severe mental illness. The authors assert that all programs contribute to this work are conformed to the Helsinki Declaration, and the ethical committee of states and institutions concerned with human experimentation. The study was approved by the Institutional Review Board of all participating medical centers (the Institutional Review Board: Clinical Trial Ethics Committee of Eastern Theater Command General Hospital; ethics approval number:2023DZKY-009-01;trial registration number: NCT05685966; data of registration: January 17,2023).

Study participants were matched by age to patients who underwent IVF–ET/ICSI–ET/FET treatment during the same period a year earlier, between November 23, 2021 and January 7, 2022, who formed the control group. All of participants signed informed consent. We recorded participants’ basic characteristics (including age, body mass index [BMI], infertility cause, AMH, and AFC) as well as cycle characteristics (treatment protocol, endometrial thickness, number of embryos transferred, embryonic morphology). Primary outcome measures were the clinical pregnancy rates (defined as an intrauterine gestational sac on ultrasound imaging), first trimester abortion rate, and live birth rate before and after the relaxation of epidemic controls. Embryo grading was based on the Istanbul consensus workshop parameters [22].

COVID-19 infection was confirmed using quantitative real-time polymerase chain reaction.

Between the 24th and 28th week of gestation, the pregnant women not previously known to have diabetes performed a diagnostic 75-g oral glucose tolerance test (OGTT). A diagnosis of GDM could be made if one or more of the following glucose levels were up to the standard: 5.1 mmol/L≤fasting<7 mmol/L, 1 h ≥ 10.0 mmol/L, and 8.5 mmol/L ≤ 2 h<11 mmol/L.

Statistical analysis

Demographic characteristics were summarized using descriptive statistics. Continuous variables are presented as mean and standard deviation or as median and interquartile range. Categorical variables are presented as number and percentage. Multivariate logistic regression analysis was used to derive unadjusted, partially adjusted, or adjusted odds ratios (ORs) and 95% confidence intervals for the association between epidemic controls or infection status and clinical outcomes. Confounders considered for partially adjusted ORs were variables with P values < 0.2 in univariate analysis. A two-tailed P value < 0.05 was considered statistically significant. Data analysis was performed using SAS statistical software (SAS Institute Inc., Cary, NC, USA).

Results

All cycles

This study included 779 women in the FET group and 168 women in the IVF–ET/ICSI–ET group (Table 1), each woman underwent a single transplantation surgery. The mean age was similar between the study and control groups, as was the mean age of participants’ partners. No differences were observed in the infertility duration, infertility type, infertility cause, or endometrial thickness; however, the mean number of embryos transferred was smaller in the FET group during 2022.

Table 1.

Participant characteristics

Characteristics	FET			ET
	2021FET(n = 467)	2022 FET(n = 312)	P value	2021ET(n = 121)		2022 ET(n = 47)	P value
Female age(year)	32.00(29.00–35.00)	32.00(29.00–35.00)	0.3924	32.00(29.00–34.00)		32.00(30.00–34.00)	0.2235
Male age(year)	32.00(30.00–36.00)	32.00(30.00–35.00)	0.8250	23.70(21.00-26.30)		22.50(21.00-25.61)	0.6909
Female BMI (kg m− 2)	23.20(20.90–26.00)	22.90(20.70-25.45)	0.1687	26.26(23.80–28.70)		24.12(21.50–26.40)	0.1580
Male BMI (kg m− 2)	25.71(23.15–27.78)	25.20(22.86–27.47)	0.1225	26.40 ± 3.48		23.90 ± 3.20	< 0.0001
Basical FSH(IU/L)	6.66(5.47–7.91)	6.50(5.40-8.00)	0.5230	3.74(2.77–5.32)		4.30(3.27–6.79)	0.1704
AMH (ng mL-1)	3.60(2.20–5.82)	3.90(2.30–6.10)	0.3087	12.00(7.00–17.00)		11.00(6.00–19.00)	0.1499
AFC	10.00(6.00–16.00)	13.00(9.00–20.00)	< 0.0001	12.00(10.00-13.40)		11.60(10.00-12.30)	0.5811
Endometrial thickness (mm)	9.50(8.70–10.30)	9.50(8.50–10.70)	0.6673	1.67 ± 0.47		1.70 ± 0.46	0.2683
Number of embryos transferred	1.36 ± 0.48	1.24 ± 0.43	0.0005	32.00(29.00–34.00)		32.00(30.00–34.00)	0.6862
Type of infertility n (%)			0.0499				0.0514
Primary	252(54.0%)	146(46.8%)		79(65.3%)		23(48.9%)
Secondary	215(46.0%)	166 (53.2%)		42(34.7%)		24(51.0%)
Endometrial preparation/COH protocol, n (%)			0.1120				0.2973
Ovulatory cycle/Agonist	23(4.9%)	24(7.7%)		75(62.0%)		25(53.2%)
Artificial cycle/Antagonist	444(95.1%)	288(92.3%)		46(38.0%)		22(46.8%)
Days of embryo transferred, n (%)			0.7085				0.2945
≤3 days	166(35.5%)	115(36.9%)		111 (91.7%)		46 (97.9%)
>3 days	301(64.5%)	197(63.1%)		10 (8.3%)		1 (2.1%)
Embryonic morphology, n (%)			0.8296				0.1428
high grade cleavage embryo	159(34.1%)	106(34.0%)		94(77.6%)		43(91.4%)
low grade cleavage embryo	18(3.8%)	11(3.5%)		17(14.0%)		3(6.3%)
High grade blastocyst	259(55.5%)	179(57.4%)		10(8.2%)		1(2.1%)
Infertility cause			0.4650				0.8912
Ovulation	81(17.3%)	53(17.0%)		11(9.1%)		5(10.6%)
Pelvic factor	248(53.1%)	170(54.5%)		70(57.9%)		23(48.9%)
Male factor	43(9.2%)	24(7.7%)		19(15.7%)		9(19.2%)
Both factors	27(5.8%)	27(8.6%)		9(7.4%)		4(8.5%)
Other	68(14.6%)	38(12.2%)		12(9.9%)		6(12.8%)

FET frozen–thawed embryo transfer, ET embryo transfer, BMI body mass index, FSH Follicle stimulating hormone, AMH Anti-Müllerian hormone, AFC Antral Follicle Counting

We applied a linear regression model for the clinical pregnancy rates, first trimester abortion rate, multiple pregnancy rate, and live birth rate in all patients. The model included patients’ basic characteristics such as age, BMI, AMH, endometrial thickness, and number of embryos transferred. The results showed no effect of control policy status on pregnancy outcomes (Table 2). However, the morbidity of gestational diabetes mellitus (GDM) after FET in 2022 was obviously higher than that in 2021 (17.8% and 6.8%, respectively).

Table 2.

Association of COVID-19 epidemic control status with pregnancy outcomes

Characteristics	Group	Percentage	Unadjusted P value OR (95%CI)	Partially-adjusted P value OR (95%CI)	Full-adjusted P value OR (95%CI)
Positive of β-HCG	2021FET	292(62.5%)	0.5906	0.3189	0.2619
	2022FET	201(64.4%)
	2021ET	69(57.0%)	0.5812	0.6334	0.5377
	2022ET	29(61.7%)
Clinical pregnant	2021FET	265(56.7%)	0.6609	0.4080	0.2161
	2022FET	182(58.3%)
	2021ET	66(54.5%)	0.8743	0.8617	0.9964
	2022ET	25(53.2%)
Ongoing pregnancy rate	2021FET	229(49.0%)	0.9306	0.8358	0.4998
	2022FET	152(48.7%)
	2021ET	57(47.1%)	0.7775	0.8405	0.9735
	2022ET	21(44.7%)
Multiple pregnancy	2021FET	39(14.7%)	0.6480	0.1936	0.5563
	2022FET	24(13.2%)
	2021ET	13(19.7%)	0.9741	0.4490	0.8614
	2022ET	5(20.0%)
Miscarriage rate	2021FET	36(13.6%)	0.3967	0.5991	0.8415
	2022FET	30(16.5%)
	2021ET	9(13.6%)	0.7738	0.8399	0.9251
	2022ET	4(16.0%)
Gestational diabetes mellitus	2021FET	15(6.8%)	0.0017	0.0037	0.0026
	2022FET	26(17.8%)
	2021ET	9(16.7%)	0.4384	0.1524	0.3845
	2022ET	2(9.5%)
Premature birth	2021FET	21(9.6%)	0.3600	0.5726	0.6697
	2022FET	10(6.8%)
	2021ET	12(22.2%)	0.3234	0.7829	0.3342
	2022ET	7(33.3%)
Live birth rate	2021FET	219(46.9%)	0.8416	0.9357	0.9014
	2022FET	146(46.8%)
	2021ET	54(44.6%)	0.9504	0.9643	0.9879
	2022ET	21(44.7%)

OR odds ratio, CI confidence interval, ET embryo transfer, FET frozen–thawed embryo transfer, HCG Human chorionic gonadotropin

Cycles after the relaxation of controls

In the analysis of clinical outcomes, we included 162 pregnant women with COVID-19 infection (22 infected before ET and 140 infected after ET) and 68 women with unconfirmed COVID-19 infection who underwent ET (including the FET group and the IVF–ET/ICSI–ET group) after the relaxation of epidemic controls (Table 3). We tested all of the women, no differences were observed between women with COVID-19 infection and those with unconfirmed COVID-19 infection (tested negative), or between infection pre- and post-ET.

Table 3.

Association of COVID-19 infection status with pregnancy outcomes

Characteristics	Group	Percentage	Unadjusted P value OR (95%CI)	Partially-adjusted P value OR (95%CI)	Full-adjusted P value OR (95%CI)
Positive of β-HCG	Uninfected(n = 98)	68(69.4%)	0.1989	0.1678	0.2349
	Infected(n = 261)	162(62.1%)
	Infected before transferred(n = 34)	22(64.7%)	0.7341	0.3258	0.2705
	Infected after transferred(n = 227)	140(61.7%)
Clinical pregnant	Uninfected(n = 98)	62(63.3%)	0.1886	0.1461	0.1878
	Infected(n = 261)	145(55.6%)
	Infected before transferred(n = 34)	18(52.9%)	0.7423	0.9939	0.9216
	Infected after transferred(n = 227)	127(55.9%)
Ongoing pregnancy rate	Uninfected(n = 98)	51(52.0%)	0.3711	0.2910	0.5337
	Infected(n = 261)	122(46.7%)
	Infected before transferred(n = 34)	17(50.0%)	0.6827	0.5743	0.7273
	Infected after transferred(n = 227)	105(46.3%)
Multiple pregnancy	Uninfected(n = 98)	10(16.1%)	0.5662	0.6901	0.7095
	Infected(n = 261)	19(13.1%)
	Infected before transferred(n = 34)	3(16.7%)	0.6331	0.7587	0.6337
	Infected after transferred(n = 227)	16(12.6%)
Miscarriage rate	Uninfected(n = 98)	11(17.7%)	0.7382	0.8265	0.5546
	Infected(n = 261)	23(15.9%)
	Infected before transferred(n = 34)	1(5.6%)	0.2287	0.3477	0.6558
	Infected after transferred(n = 227)	22(17.3%)
Gestational diabetes mellitus	Uninfected(n = 98)	6(12.0%)	0.2850	0.3560	0.4251
	Infected(n = 261)	22(18.8%)
	Infected before transferred(n = 34)	2(11.8%)	0.4281	0.3193	0.0514
	Infected after transferred(n = 227)	20(20.0%)
Premature birth	Uninfected(n = 98)	4(8.0%)	0.5446	0.5552	0.5335
	Infected(n = 261)	13(11.1%)
	Infected before transferred(n = 34)	3(17.6%)	0.3605	0.3587	0.4680
	Infected after transferred(n = 227)	10(10.0%)
live birth rate	Uninfected(n = 98)	50(51.0%)	0.4933	0.6416	0.8433
	Infected(n = 261)	117(44.8%)
	Infected before transferred(n = 34)	17(50.0%)	0.9698	0.9661	0.8719
	Infected after transferred(n = 227)	100(44.1%)

OR odds ratio, CI confidence interval, HCG Human chorionic gonadotropin

Similarly, pregnant women’s vaccination status was not associated with pregnancy outcomes or GDM. Additionally, symptoms accompanying COVID-19 infection (olfactory change, taste change, or fever) were not associated with pregnancy outcomes or GDM (Supplementary 1).

Discussion

In our retrospective cohort study, the relaxation of COVID-19 epidemic control policies had no impact on the outcomes of fresh IVF–ET/ICSI–ET/FET treatment in terms of the biochemical pregnancy rate, clinical pregnancy rate, ongoing pregnancy rate, first trimester abortion rate, and live birth rate.

The COVID-19 pandemic had a profound impact on patients preparing for IVF–ET because treatments in many countries were suspended to prevent the spread of infection. The purpose of our study was to examine whether the relaxation of epidemic control policies had a measurable effect on IVF treatment outcomes. To the best of our knowledge, this is the first study to date reporting the effect of epidemic control policies on IVF treatment outcomes in China.

SARS-CoV2 enters cells via the ACE-2 cellular receptor and the TMPRSS2 cellular protease, which are expressed in the granulosa cells, in follicular maturation, and in the endometrium [23–26]. SARS-CoV-1 is reportedly associated with a high maternal mortality rate, early miscarriage, and intrauterine growth restriction [27]. SARS-CoV-2 infection may also influence clinical outcomes.

In our study, we evaluated important targets including the pregnancy rate, ongoing pregnancy rate, first trimester abortion rate, and live birth rate. No difference was observed in any investigated outcomes after the relaxation of epidemic control policies. These results were consistent in a logistic regression model of clinical outcomes, indicating that lifting of epidemic control policies in China did not compromise IVF–ET/ICSI–ET/FET outcomes.

Previous reports have focused on the difference between groups with and without COVID-19 infection; however, the infection rate increased rapidly after relaxation of the epidemic control policies in China. Importantly, some patients had false-negative test results or were asymptomatic; therefore, the actual number of COVID-19 infections was likely higher. Real-world clinical data from previous studies showed that antibody tests had a high specificity for detecting SARS-CoV-2; nevertheless, the sensitivity among testing kits varied from 57.24% to 93.3% [28–32]. We therefore selected patients who underwent ET between November 23, 2022 to January 7, 2023, a period when epidemic controls had recently been lifted. We then compared these patients with patients from the previous year to reveal differences in outcomes after the lifting of COVID-19 epidemic control policies.

Considering that COVID-19 infection affects multiple tissues and organs, we found no significant differences in the rates of ongoing pregnancy or live birth rate according to our data. However, we found that the rate of GDM with FET after relaxation of epidemic controls was higher than that in the previous year. A study in West Virginia also showed that GDM prevalence was higher during COVID-19 pandemic compared to pre-pandemic (8.59% vs. 7.77%) [33]. Another study in Northeast Italy reveled that GDM prevalence during the COVID-19 pandemic was significantly higher than last year (9% vs. 13.5%) [34]. GDM may exacerbate course of COVID-19 and vice versa [35, 36].

GDM is a serious complication of pregnancy, in which the pregnant woman develops chronic hyperglycemia during gestation, without having previously diagnosed diabetes [37]. GDM is mostly the result of impaired glucose tolerance owing to pancreatic β-cell dysfunction. However, low-grade chronic inflammation [38–41] and oxidative stress [42–45] may contribute to the pathology of GDM, both of which are present in COVID-19 infection and may contribute to symptom persistence following acute illness [46–48]. And SARS-CoV-2 may target the pancreas and placenta through ACE-2 cellular receptor, contributing to maternal β-cell dysfunction [49–51]. A meta-analysis showed that the reported incidence of GDM in China is 11.91% [52], and the prevalence of GDM varies across different cities (from 2.3% to 24.24%) [53]. In our study, we found that the incidence of GDM was higher than the incidence 1 year earlier (6.8%,15/219) in the FET group after the relaxation of epidemic controls (17.8%,26/146), which may be owing to analogous pathogenesis. However, the lifestyle changes, stress levels, dietary, or care-access factors after the outbreak of the epidemic might also be the causes. Further research on the underlying mechanisms is needed to explain this phenomenon. The low incidence of GDM in our control group may be owing to the younger mean age (31 years) of our study participants and/or differences in different regions of China.

Interestingly, we found that the rate of GDM showed no differences between women with and without confirmed COVID-19 infection and was not associated with the accompanying symptoms of COVID-19. This may be because the actual COVID-19 infection rate was higher than our clinical data owing to the accuracy of test kits. Meanwhile, the limitations of our study also should be cautious, we didn’t analysis the parity, family history of diabetes, PCOS, steroid use, frozen cycle preparation method and so on, the confounders need more deeper research to eliminate. And the stress levels, lifestyle behaviors, IVF laboratory practice evolution might be differed between years.

Despite our findings, the long-term effects on offspring are unknown. Studies are needed that include long-term follow-up of the offspring of pregnant women after the relaxation of epidemic controls.

In conclusion, our findings showed that relaxation of COVID-19 epidemic control policies in China had no influence on the clinical pregnancy rate, ongoing pregnancy rate, and live birth rate. Nevertheless, the morbidity of GDM in FET cycles after the relaxation of controls was higher than the rate 1 year earlier. Further studies are warranted to support these findings, with a particular focus on long-term effects in the children of women infected with SARS-CoV-2 who received ART treatment.

Abbreviations

IVF

In vitro Fertilization

ET

Embryo Transfer

ICSI

Intracytoplasmic Sperm Injection

FET

Frozen–thawed Embryo Transfer

AMH

Anti-müllerian Hormone

BMI

Body Mass Index

AFC

Antral Follicle Counting

GDM

Gestational Diabetes Mellitus

ART

Assisted Reproductive Technology

ORs

Odds Ratios

PCOS

Polycystic Ovary Syndrome

Authors’ contributions

CZ, JD, MB: analysis and interpretation of data; MZ, provided statistical support. YL, BY, LC: contributions to the conception, design of the work. Each author has approved the submitted version and have agreed both to be personally accountable for the author’s own contributions and to ensure that questions related to the accuracy or integrity of any part of the work.

Funding

This study was supported by the National Natural Science Foundation of China (No.81973965 and No.82274651), Medical Scientific Research Key Project of Jiangsu Commission of Health (ZD2022004), and Jiangsu Provincial Medical Key Discipline Cultivation Unit(JSDW202215).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Institutional Review Board of all participating medical centers.

Consent for publication

The manuscript has been read and approved by all authors.

Competing interests

The authors declare no competing interests.