Introduction
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly contagious and pathogenic coronavirus that first appeared in late 2019 and has caused a pandemic of acute respiratory disease, named “coronavirus disease 2019 (COVID-19)”, with over 620 million confirmed cases and more than 6.6 million fatalities in nearly 200 countries (Updated information from the World Health Organization [WHO], as on November 1, 2022, https://covid19.who.int [1] [2] [3]
Most reproductive treatments had to be halted worldwide due to the COVID-19 outbreak.[4] [5]
Inactivated vaccine, live attenuated vaccine, recombinant subunit vaccine, recombinant viral vector vaccine, DNA vaccine, and RNA vaccine for COVID-19 have been developed and put into use one after another, with inactivated vaccines being the most frequently used in China and many other nations.[6] [7] vaccination in pregnant women when the benefits of vaccination to the pregnant woman outweigh the potential risks for the long-term safety. In reality, there is yet no conclusion for how immunization could alter the results of assisted reproductive technology (ART). To provide statistical support for recommendations for COVID-19 vaccination in in vitro fertilization–embryo transfer (IVF–ET) procedure, our study investigated the influence of vaccination against COVID-19 in infertile populations on the results of their IVF–ET.
Methods
Ethics approval
The study was approved by the Peking University Third Hospital Ethics Committee (No. 2018S2-002) and performed according to the ethical principles of the Declaration of Helsinki . Patients provided written consent for the information to be used in the analyses, editing, and publications.
Study design and participants
A single-center retrospective cohort study was conducted in 10,541 IVF–ET cycles from June 2020 to August 2021 at Peking University Third Hospital Reproductive Medical Center. We screened 835 IVF cycles from infertile couples with a history of vaccination against COVID-19 before assisted reproductive therapy. The cohort study utilized the Matchlt package of R software (http://www.R-project.org/
Vaccination groups were divided into three groups according to gender, namely group of vaccination of only females (Group F, n = 75), group of vaccination of only males (Group M, n = 484), and group of vaccination of both genders (Group B, n = 276). All the IVF–ET cycles of vaccinated females were divided into three subgroups according to vaccine types, namely recombinant adenovirus vaccine group (n = 68), inactivated virus vaccine group (n = 278), and recombinant subunit vaccine group (n = 5) [Figure 1 ].
Figure 1: The flowchart of the selection of patients received in vitro fertilization–embryo transfer (IVF–ET) with or without vaccination against COVID-19. COVID-19: Coronovirus disease 2019; ET: Embryo transfer; IVF: In vitro fertilization.
Assisted reproduction techniques
Controlled ovarian hyperstimulation, oocyte recovery, intracytoplasmic sperm injection (ICSI) technique, embryo culture, and morphological assessment of embryos were performed. Embryo transfer (ET) was generally performed 72 h or 120 h after oocyte collection.
Outcome measures
The primary outcomes were the number of oocytes retrieved, fertilization rate (defined as the ratio between the number of fertilized oocytes and the total number of oocytes retrieved), cleavage rate (defined as the ratio between the number of cleaved embryos and the number of fertilized oocytes), 2 pronuclei (2PN) rate (defined as the ratio between the number of oocytes containing 2PN and the number of oocytes retrieved. 2PN was defined as the presence of two clearly distinct pronuclei and two polar bodies), good-quality embryo rate (defined as the ratio between a total number of good-quality embryos formed and the number of embryos cultured up to days 3–7). Embryo quality was evaluated on Day 3, and good-quality embryo referred to an embryo with >5 cells, symmetric blastomeres with respect to size and shape, and with <10% of the volume of the embryo fragmented in our research.
The secondary outcomes were related to pregnancy outcomes. Clinical pregnancy was defined as the presence of a gestational sac under ultrasonography, and biochemical pregnancy was defined as two occurrences of human chorionic gonadotropin (hCG) levels >5 mU/mL 15 days or more after hCG injection without clinical pregnancy establishment.
Statistical analysis
A 1:2 propensity score matching was utilized to reduce unbalanced baseline characteristics between the vaccinated and unvaccinated groups. The match was conducted using the nearest-neighbor matching algorithm. Propensity scores were calculated using logistic regression with the following covariates: type of infertility, age of the spouses, duration of infertility, times of pregnancies, times of deliveries, body mass index (BMI), basal-follicle-stimulating hormone (FSH), basal-estradiol (E2), basal-luteinizing hormone (LH), anti-müllerian hormone (AMH), antral follicle count (AFC), protocol of controlled ovarian hyperstimulation, duration of gonadotrophin (Gn) applied, and total Gn applied.
For the quantitative data, the Kolmogorov–Smirnov method was used to test for normal distribution. The quantitative elements were expressed as mean±standard deviation. For the qualitative data, n (%) was used to express them. Statistical tests were done with R software (version 3.6.0; R Foundation for Statistical Computing, Vienna, Austria) and SPSS (version 25.0; Chicago, IL, USA). Statistical significance was set at two-sided P -value <0.05.
Results
A total of 10,541 IVF cycles were included in this study, of which one or both couples had been vaccinated against COVID-19 with a total of 835 cycles, and an additional 1670 cycles were statistically matched for analysis as the control group.
Patient baseline characteristics during IVF–ET treatment, including age of female/male, duration of infertility, type of infertility, BMI, controlled ovarian hyperstimulation regimen, and other parameters are shown in Table 1 . All the characteristics were comparable between the groups.
Table 1 -
Baseline characteristics of the participants received IVF-ET treatment with or without
vaccination against COVID-19.
Variables
Vaccinated group (n = 835)
Unvaccinated group (n = 1670)
Statistics
P -value
Female age (years)
34.83 ± 4.82
34.79 ± 4.76
0.225
0.822
Male age (years)
36.11 ± 5.63
36.20 ± 5.93
−0.378
0.706
Duration of infertility (years)
3 (1, 24)
3 (0, 20)
−0.969
0.333
Types of infertility
0.541
0.462
Primary infertility
444 (53.2)
862 (51.6)
Secondary infertility
391 (46.8)
808 (48.4)
Gravidity (times)
0 (0, 6)
0 (0, 7)
0.567
0.571
Delivery (times)
3.094
0.213
0
710 (85.0)
1416 (84.8)
1
121 (14.5)
234 (14.0)
2
4 (0.5)
20 (1.2)
BMI (kg/m2 )
22.64 ± 3.44
22.73 ± 3.32
−0.631
0.528
Basal FSH (mIU/mL)
6.84 (0.10, 24.90)
6.71 (0.18, 31.20)
−0.060
0.952
Basal E2 (mmol/L)
154 (23.00, 983.00)
154.5 (1.42, 2136.00)
−1.404
0.160
Basal LH (mIU/mL)
3.22 (0.10, 28.80)
3.3 (0.18, 35.90)
0.735
0.462
AMH (ng/mL)
1.87 (0.01, 21.22)
1.85 (0.01, 27.12)
−0.104
0.917
AFC
9.50 ± 6.14
9.69 ± 5.79
−0.767
0.443
Protocol of controlled ovarian hyperstimulation
7.598
0.055
Long GnRH agonist
125 (15.0)
233 (14.0)
Ultralong GnRH agonist
46 (5.5)
119 (7.1)
GnRH antagonist
628 (75.2)
1274 (76.3)
Others
36 (4.3)
44 (2.6)
Duration of Gn applied (days)
10.5 ± 2.4
10.6 ± 2.3
−0.733
0.464
Total Gn applied (units)
2797.47 ± 1197.23
2786.47 ± 1145.00
0.223
0.823
Type of fertilization∗
2.341
0.511
IVF
483/818 (59.1)
992/1637 (60.6)
ICSI
323/818 (39.5)
613/1637 (37.5)
Half-ICSI
6/822 (0.7)
21/1637 (1.3)
Rescue ICSI
6/822 (0.7)
11/1637 (0.7)
Type of transferred embryo†
0.176
0.674
Cleavage embryo
356/366 (97.3)
790/816 (96.8)
Blastocyst
10/366 (2.7)
26/816 (3.2)
Number of embryo transferred
1.79 ± 0.41
1.79 ± 0.41
−0.032
0.974
Data are presented as n (%), mean ± standard deviation, or median (interquartile range).
∗ The vaccinated group completed 818 times of fertilization and another six times of respective half-ICSI and rescue ICSI (n = 822), and the unvaccinated group completed 1637 times of fertilization.
† The vaccinated group has a total of 366 ET cycles and the unvaccinated group has 816 ET cycles. AFC: Antral follicle count; AMH: Anti-müllerian hormone; BMI: Body mass index; COVID-19: Coronovirus disease 2019; E2: Estradiol; FSH: Follicle-stimulating hormone; Gn: Gonadotropin; GnRH: Gonadotropin-releasing hormone; ICSI: Intracytoplasmic sperm injection; IVF: In vitro fertilization; IVF-ET: In vitro fertilization and embryo transfer; LH: Luteinizing hormone.
There was no statistically significant difference between the vaccinated group and the unvaccinated group in the number of oocytes obtained and indicators related to embryo development, such as cleavage rate, good-quality embryo rate, etc . Also, a total of 366 ET cycles in the vaccinated group and 816 ET cycles in the non-vaccinated group were recorded, with clinical pregnancy rates of 42.4% (155/366) and 40.2% (328/816) in the two groups (P = 0.486) and the biochemical pregnancy rate was similar in both groups [Table 2 ].
Table 2 -
Embryology outcomes and clinical reproductive outcomes of 2505 oocyte retrieval cycles, comparing patients vaccinated or unvaccinated against COVID-19.
Variables
Vaccinated group (n = 835)
Unvaccinated group (n = 1670)
Statistics
P -value
Number of oocytes collected
8.00 (0, 40.00)
9.00 (0, 77.00)
−1.795
0.073
Cleavage rate
0.98 ± 0.07
0.98 ± 0.08
0.760
0.447
Fertilization rate
0.77 ± 0.23
0.76 ± 0.23
1.063
0.288
2PN rate
0.58 ± 0.26
0.57 ± 0.26
0.728
0.467
Good-quality embryo rate
0.56 ± 0.32
0.56 ± 0.31
−0.045
0.964
Biochemical pregnancy rate∗
26/366 (7.1)
71/816 (8.7)
0.856
0.355
Clinical pregnancy rate∗
155/366 (42.4)
328/816 (40.2)
0.485
0.486
Data are presented as n (%), mean ± standard deviation, or median (interquartile range).
∗ Clinical pregnancy rate and biochemical pregnancy rate are calculated per ET cycle. Vaccinated group has a total of 366 ET cycles and unvaccinated group has 816 ET cycles. COVID-19: Coronovirus disease 2019; ET: Embryo transfer; 2PN: 2 pronuclei (the presence of two clearly distinct pronuclei and two polar bodies).
Gender-based subgroup analysis showed that vaccination of different genders also had no statistically significant effect on the outcomes of ART. The vaccination group completed 366 ET cycles, of which 28 cycles were from Group F, 217 cycles from Group M, and 121 cycles from Group B. The clinical pregnancy rates of Group F, Group M, and Group B were 46.4% (13/28), 41.0% (89/217), and 43.8% (53/121), respectively. Meanwhile, the outcome of embryo development was similar between different groups [Table 3 ].
Table 3 -
Embryology outcomes and clinical reproductive outcomes of 835 oocyte retrieval cycles, comparing gender-specific vaccinations against COVID-19.
Variables
Group of vaccination of only females (Group F, n = 75)
Group of vaccination of only males (Group M, n = 484)
Group of vaccination of both genders (Group B, n = 276)
Statistics
P -value
Number of oocytes collected
11.00 (1.00, 34.00)
8.00 (0, 36.00)
8.00 (0, 40.00)
1.182
0.307
Cleavage rate
0.97 ± 0.14
0.99 ± 0.06
0.99 ± 0.06
2.244
0.107
Fertilization rate
0.79 ± 0.23
0.77 ± 0.23
0.77 ± 0.24
0.345
0.708
2PN rate
0.61 ± 0.26
0.59 ± 0.26
0.60 ± 0.27
1.051
0.350
Good-quality embryo rate
0.63 ± 0.31
0.55 ± 0.31
0.56 ± 0.33
1.875
0.154
Biochemical pregnancy rate∗
3/28 (10.7)
10/217 (4.6)
13/121 (10.7)
5.343
0.055
Clinical pregnancy rate∗
13/28 (46.4)
89/217 (41.0)
53/121 (43.8)
0.454
0.797
Data are presented as n (%), mean ± standard deviation, or median (interquartile range).
∗ Clinical pregnancy rate and biochemical pregnancy rate are calculated per ET cycle. The vaccination group completed 366 ET cycles, of which 28 cycles were from Group F, 217 cycles from Group M, and 121 cycles from Group B. COVID-19: Coronovirus disease 2019; ET: Embryo transfer; 2PN: 2 pronuclei (the presence of two clearly distinct pronuclei and two polar bodies).
We also conducted a subgroup analysis in different types of vaccines of Group F and Group B, including the adenovirus vaccine group and the inactivated vaccine group. The recombinant subunit vaccine group was not involved in the analysis due to a limited number of cases. Analysis of data from 346 oocyte retrieval cycles and 147 ET cycles of vaccinated females revealed that there was no difference between adenovirus vaccine and inactivated vaccine on the clinical outcome of ART [Table 4 ].
Table 4 -
Embryology outcomes and clinical reproductive outcomes of 346 oocyte retrieval cycles, comparing inactivated vaccine and adenovirus vaccine against COVID-19.
Variables
Recombinant adenovirus vaccine group (n = 68)
Inactivated vaccine group (n = 278)
Statistics
P -value
Number of oocytes collected
8.00 (0, 34.00)
9.00 (1.00, 40.00)
0.822
0.412
Cleavage rate
0.98 ± 0.07
0.98 ± 0.09
−0.146
0.884
Fertilization rate
0.80 ± 0.25
0.77 ± 0.23
0.862
0.389
2PN rate
0.60 ± 0.28
0.57 ± 0.26
0.905
0.366
Good-quality embryo rate
0.58 ± 0.36
0.58 ± 0.32
0.111
0.912
Biochemical pregnancy rate∗
1/24 (4.2)
13/123 (10.6)
0.955
0.468
Clinical pregnancy rate∗
13/24 (54.2)
53/123 (43.1)
0.996
0.318
Data are presented as n (%), mean ± standard deviation, or median (interquartile range).
∗ Clinical pregnancy rate and biochemical pregnancy rate are calculated per transplant cycle. The vaccinated females completed 147 ET cycles, of which 24 cycles were from recombinant adenovirus vaccine group and 123 cycles from inactivated vaccine group. COVID-19: Coronovirus disease 2019; ET: Embryo transfer; 2PN: 2 pronuclei (the presence of two clearly distinct pronuclei and two polar bodies).
Discussion
Infections of SARS-CoV-2 can occur in a range of female organs and tissues through combination with the widely expressed angiotensin-converting enzyme 2 (ACE2), which may increase the risk of female reproductive organ dysfunction.[8,9] vaccination could reduce the risk of SARS-CoV-2 infections in couples receiving ART, as well as alleviate the reproductive health damage caused by emergent panic psychology;[10]
In this study, we examined three main considerations for patients undergoing IVF–ET: vaccination or not, vaccination type, and gender of vaccination population. The results of ART and embryonic development were unaffected by vaccination when there were no appreciable changes in the fundamental traits of the various demographic groups analyzed. None of the participants in our research who have accepted ART treatment had ever been exposed to the coronavirus since the COVID-19 pandemic in China was successfully contained in the second quarter of 2020.[11] vaccination deserves to be encouraged because it does not worsen the outcome of ART.
The number of vaccination of only females was 75, while the number was 484 for males. The number of vaccination for both genders was 276, apparently lower than the number of vaccination of only males. The proportion of women vaccinated in infertile couples is significantly lower than that of men vaccinated due to the important role of females in childbirth and lactation, whereas our results show that the vaccinations for COVID-19 of different genders have no significant impact on IVF–ET outcomes and the development of follicles and embryos. The available evidence has shown that the adverse effects of SARS-CoV-2 infection on the male reproductive system are limited, and few studies have reported the semen analysis results or the presence of viral RNA in semen samples of infected men.[12,13] [14] [15] [16–18] et al [19] [19] vaccination had no statistically significant effect on the IVF–ET outcomes by gender, vaccination against COVID-19 can be recommended before IVF-ET treatment regardless of gender.
This study also examined the impact of vaccination with various vaccine types, primarily recombinant adenovirus vaccines and inactivated vaccines, on the success rate of IVF–ET. Adenovirus-based vaccines were prepared by inserting a transgene cassette into the adenoviral backbone through direct cloning or homologous recombination. The transgene cassette expressed the target antigen under the control of a strong promoter that was capable of maintaining robust and sustained expression of the transgene.[20] [21] vaccination type is not an influencing factor during assisted reproductive treatment.
In conclusion, this study demonstrated that vaccination status had no statistically significant impact on the success rate of IVF–ET or the growth of follicles and embryos. Moreover, different types of vaccine (inactivated vaccine or recombinant adenovirus vaccine) also had no statistically significant effect on clinical outcomes of IVF–ET. Vaccination against COVID-19 before accepting IVF–ET treatment should be encouraged. These findings provided theoretical support for the application of COVID-19 vaccines in ART during the pandemic. As a single-center retrospective study, it should be highlighted that this research needs to be further confirmed by prospective studies using suitably large sample sizes.
Funding
This work was supported by the National Science Fund for Distinguished Young Scholars (No. 81925013) and the Incubation Foundation for Young Scientists of the Peking University Third Hospital (No. BYSYFY2021048).
Conflicts of interest
None.
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