Outcomes Between Fresh Embryo and First Frozen-Thawed Embryo Transfer in Donor Sperm In-Vitro Fertilisation

By Jiayao Chen¹, Zhiping Zhang², Wenjing Shi¹, Qin Yan¹, Shimin Wang¹, Xueqing Wu²

Affiliations

1. Department of Clinical Discipline Construction Centre, Shanxi Medical University, Taiyuan, Shanxi, China
2. Reproductive Medicine Centre, Children’s Hospital of Shanxi and Women Health Centre of Shanxi, Affiliated Hospital of Shanxi Medical University, Taiyuan, China

doi: 10.29271/jcpsp.2025.06.703

ABSTRACT
Objective: To compare the pregnancy outcomes of embryo transfer (ET) and frozen-thawed embryo transfer (FET) after controlling for maternal confounding factors.
Study Design: Descriptive analytical study.
Place and Duration of the Study: Reproductive Medicine Centre, Children’s Hospital of Shanxi and Women Health Centre of Shanxi, Affiliated Hospital of Shanxi Medical University, Taiyuan, China, from January 2015 to September 2022.
Methodology: Clinical data and pregnancy outcomes of 1,051 sperm-donor in-vitro fertilisation IVF/ICSI embryo-transfer cycles, divided into initial FET and fresh ET groups, were compared. Primary outcomes included clinical pregnancy rate, miscarriage rate, and live birth rate.
Results: Significant differences were observed in clinical pregnancy and live birth rates (44.02% vs. 53.63%, p = 0.018; 34.78% vs. 44.87%, p = 0.012) but not in miscarriage or ectopic pregnancy rates (18.52% vs. 14.41%, p = 0.339; 2.47% vs. 1.94%, p = 0.752) between the groups.
Conclusion: In 1,065 sperm-donor IVF cycles, frozen-thawed embryos yielded higher clinical pregnancy and live birth rates, particularly with single ET. FET is a successful, safe, and preferable option for couples using donor sperm in assisted reproductive technologies.

Key Words: Donor sperm, Fresh embryo transfer, Frozen–thawed embryo transfer, Pregnancy outcome, Assisted reproductive technique.

INTRODUCTION

In assisted reproductive technology, in-vitro fertilisation- embryIo transfer (IVF-ET) and intracytoplasmic sperm injection (ICSI) are feasible for assisted conception, where fresh embryo transfer (ET) or frozen-thawed embryo transfer (FET) can be used. The first successful FET took place about 40 years ago, and since then it has rapidly developed from being viewed as a fresh cycle supplement to a significant therapeutic alternative in the area of assisted reproduction. The number of FET rose by 82.5% between 2006 and 2012, whereas the number of fresh ET increased by only 3.1%, according to a report by the Society for Assisted Reproductive Technology (SART).¹

There is a growing evidence that in infertile populations, FET performs better than ET. This is primarily because frozen embryos are delayed for transfer until the next cycle without ovarian stimulation, which can be effective in reducing the incidence of ovarian hyperstimulation syndrome (OHSS). Therefore, it is crucial for infertile couples to use a variety of IVF techniques. Although there have been numerous prior studies on the variables influencing the pregnancy outcome of FET, the main emphasis has been on the influence of female factors, such as endometrial thickness, uterine factors (e.g., endometrial hyperplasia or endometrial polyps), and progesterone levels. However, the pregnancy outcome of frozen-thawed embryos is still controversial. According to the literature reviewed, few researchers have looked further into how frozen embryos affect pregnancy outcomes after controlling for maternal confounding factors. Few significant studies on pregnancy outcomes with donor sperm have been published. The advantage of using donor sperm is that it preserves the female partner's normal fertility and ovarian activity in male- factor infertile couples. Additionally, choosing donor sperm eliminates the impact of semen on embryo quality, allowing for better comparisons of pregnancy outcomes between the two groups and a more thorough investigation of whether the freezing and thawing process has an impact. This study aimed to determine the pregnancy outcomes of ET and the first FET in in-vitro assisted reproductive technologies for male infertile couples.

METHODOLOGY

Clinical data from 1,051 donor sperm IVF/ICSI cycles (from January 2015 to September 2022) at the Centre of Reproductive Medicine at Shanxi Children's Hospital and Women Health Centre, were retrospectively analysed. In this descriptive analytical study, data were collected from the mutual creation of an assisted reproductive management system, a registration system to ensure the accuracy and completeness of the assisted reproductive data. Inclusion criteria were male spouse infertility, seminal fluid obtained from sperm banks for humans that the former National Health and Family Planning Commission approved, satisfying the requirements of having at least 40% of forward-moving spermatozoa (a+b) after cryo-resuscitation and a maximum of 12×10⁶ forward-moving spermatozoa per seminal fluid,² and FET group selected for first-cycle transfer. Exclusion criteria were women with endometrial abnormalities, endocrine diseases (hypothyroidism, hyperthyroidism, diabetes, and hyperprolactinemia), recurrent miscarriage, chromosomal abnormalities, receive preimplantation genetic testing, long-term smoking and drinking, and long-term use of certain agents for example; antidepressants or non-steroidal anti-inflammatory medicines that may affect fertility (Figure 1). This study was conducted retrospectively from data obtained for clinical purposes. Ethical approval for this study was granted by the Bioethics Committee of the Children’s Hospital of Shanxi and Women Health Centre, China (IRB-WZ-2024-013). 

Most patients underwent controlled ovulation hyperstimulation (COH) using long and short protocols, and a few used antagonist protocols, GnRH alone protocols, or ultra-long protocols, based on the patient's age and hormone levels. IVF or ICSI fertilisation was used 4-6 hours after egg retrieval. Normal fertilised eggs were further considered for ET or freezing for conservation. A vitrification freezing protocol was used for all frozen embryos.

Each group's age, years of infertility, BMI, basal FSH and LH values, total GnRH dosage and total GnRH number of days, number of eggs extracted, pregnancy rate, miscarriage rate, and live birth rate were totalled. Important determinants of the effectiveness of ART are the pregnancy rate and live birth rate. Pregnancy rate = number of cycles of pregnancy / number of cycles of all embryo transplants × 100%. Miscarriage rate = number of cycles with miscarriage / number of all clinical pregnancy cycles × 100%. Live birth rate = number of cycles with live birth / number of all clinical pregnancy cycles × 100%. Positive blood HCG levels and ultrasound images of the developing fetus and primitive heart tube pulsation were used to define clinical pregnancy. When a foetal heartbeat was detected via ultrasound before 28 weeks of pregnancy and the pregnancy was terminated, the word abortion was used. A live birth is one in which the fetus is delivered with one of the four vital signs (respiration, heartbeat, umbilical cord pulsation, and contraction of voluntary muscles) and takes place after 28 weeks of gestation (or when the baby weighs 1,000g or more).

SPSS version 26.0 was used to analyse the data. Measurements were expressed as mean ± standard deviation (SD); to compare the quantitative variables, the student’s t-test for independent samples was used, variables that were categorical, were expressed as frequencies and percentages (%), and differences between groups were tested using the χ² test, with a continuity correction for the presence of 1 <T <5, significance at p <0.05.

RESULTS

The difference between the two groups was significant in terms of age, basic FSH, total GnRH days, and number of oocytes retrieved (Table I). Differences in years of infertility, BMI, basal LH values, and total GnRH dosage were not significant (Table I). The difference in clinical pregnancy rate and live birth rate between fresh ET and FET was significant (44.02% versus 53.63%, p = 0.018; 34.78% versus 44.87%, p = 0.012), and the difference in the miscarriage rate and ectopic pregnancy was not found to be significant (Table II). Among the different types of embryo subgroups and different groups of the number of embryos transferred, the clinical pregnancy rate and live birth rate in FET were higher than those in fresh ET, and the miscarriage rate was lower than that in fresh ET (Table III).

Table I: Comparison of general information of the two groups.
 

Variables	ET	FET	p-value
Age (years)	30.19 ± 4.45	29.12 ± 3.70	0.003*
Years of infertility	4.29 ± 3.31	4.41 ± 3.14	0.645
BMI (kg/m2)	22.90 ± 4.14	22.86 ± 3.21	0.892
Basic FSH	8.82 ± 4.06	7.67 ± 5.41	0.007*
Basic LH	5.15 ± 9.36	4.18 ± 3.07	0.168
Total GnRH dosage	3013.84 ± 1106.30	3139.51 ± 983.45	0.155
Total GnRH days	10.69 ± 2.50	11.21 ± 3.26	0.041*
Number of oocytes retrieved	10.39 ± 4.83	18.02 ± 9.94	<0.001*
*p-value <0.05; independent t-test.

Table II: Comparison of pregnancy outcomes between the two groups.

Variables	ET	FET	p-value
Clinical pregnancy (n, %)	81/184 (44.02%)	465/867 (53.63%)	0.018*
Miscarriage rate (n, %)	15/81 (18.52%)	67/465 (14.41%)	0.339
Live birth (n, %)	64/184 (34.78%)	389/867 (44.87%)	0.012*
Ectopic pregnancy	2/81 (2.47%)	9/465 (1.94%)	0.752
*p-value <0.05; χ2 test.

Table III: Comparison of pregnancy outcomes of different types and numbers of embryos between the two groups.

Variables		Clinical pregnancy (n, %)	Miscarriage rate (n, %)	Live birth (n, %)
D3 embryos	ET	56/138 (40.58%)	8/56 (14.29%)	46/138 (33.33%)
	FET	245/489 (50.1%)	28/245 (11.43%)	216/489 (44.17%)
	p-value	0.048*	0.552	0.023*
D5 or D6 blastocysts	ET	24/43 (55.81%)	7/24 (29.17%)	17/43 (39.53%)
	FET	203/33 (59.88%)	38/203 (18.72%)	159/339 (46.90%)
	p-value	0.609	0.346a	0.361
Number of embryos transferred is 1	ET	12/47 (25.53%)	4/12 (33.33%)	8/47 (17.02%)
	FET	39/111 (35.14%)	3/39 (7.69%)	35/111 (31.53%)
	p-value	0.238	0.075a	0.061
Number of embryos transferred >1	ET	69/137 (50.36%)	11/69 (15.94%)	56/137 (40.88%)
	FET	424/756 (56.08%)	64/424 (15.09%)	354/756 (46.83%)
	p-value	0.215	0.856	0.199
*p-value <0.05 ; a Continuity correction; χ2 test.

Figure 1: Data selection process for the analysis of pregnancy out- comes in this study.

DISCUSSION

In the present study, it was discovered that FET's clinical pregnancy rate and live birth rate were significantly greater than those of fresh ET. Compared to the group receiving fresh ET, the miscarriage rate was much lower, while the difference was not statistically significant. The views expressed in this article are compatible with the majority of contemporary beliefs, which hold that FET is preferable than ET in terms of the outcomes of in-vitro-assisted reproductive technologies. The first randomised experiment concentrating on clinical results was carried out in 2011 by Shapiro et al.³ They discovered that clinical pregnancy rates were higher with FET than with fresh ET. Matheus Roque hypothesised that FET results in higher continuing pregnancy rates, better clinical outcomes, and fewer perinatal problems in their investi-gations in 2015.⁴ The same argument has been made in numerous later randomised clinical investigations.⁵

Prerequisites for successful implantation are an implantable embryo and good embryo-endometrial synchronisation. E₂ and progesterone (P₄) act on endometrial development and maturation, respectively, in fresh transfer of embryo cycles. COH causes premature elevation of P₄ and high E₂ levels, which allows for the early closure of the implantation window and results in embryo-endometrial dyssynchronisation.⁶

In FET cycles, frozen preserved embryos are transferred 3 to 5 days after ovulation during a regular menstrual cycle, which is regarded as a natural transfer. The advantage of this approach is that by implanting the embryo when hormone levels are back to normal, the endometrium becomes more physiologic, thus improving endometrial tolerance, increasing pregnancy rates, decreasing maternal and perinatal morbidity, and avoiding ovarian hyperstimulation. The clinical pregnancy rate of frozen-thawed embryos is further increased by the fact that the freezing and thawing process function as a filter for low-quality embryos, allowing viable embryos to be deemed high-quality embryos.

Abortions occur naturally in about 10 to 15% of pregnancies. In assisted reproduction pregnancies, the miscarriage rate is about 20%, which is generally higher than the miscarriage rate in natural pregnancies.^7,8 This may be related to the fact that assisted reproductive technology uses in-vitro techniques to intervene in the normal fertility process and that infertile couples are in worse physical condition than normal couples. The comparison of miscarriage rates between fresh ET and FET has produced inconsistent results. The risk of miscarriage is generally higher when frozen-thawed embryos are transferred than when FE are. The early miscarriage rates in fresh ET and FET were 16.2% versus 18.5%, according to Wang et al.'s in-vitro analysis of 3,161 pregnant women with singleton pregnancies.⁹ According to Yang et al.,¹⁰ the miscarriage rate was 21.59% in the group receiving freeze-thawed embryos compared to 17.19% in the group receiving fresh embryos. However, a growing number of studies indicate that transferring the frozen-thawed embryos reduces the risk of miscarriage. According to Wang et al.,¹¹ the miscarriage rate in the group receiving FET was 6.52%, which was considerably lower than the 14.01% rate in the group receiving fresh ET. The loss rates for fresh ET and FET were 14.1% and 12.8%, according to a research by Ozgur et al.¹²

In this study, fresh ET had a miscarriage rate of 18.52% while FET had 14.41%, although the difference was not statistically significant (p = 0.339). A review of the literature shows that pelvic tubal factors, cervical factors, endometriosis, and ovulatory disorders largely contribute to female infertility and miscarriage. The addition of donor sperm in the current study, where the majority of patients were healthy women, resulted in a lower miscarriage rate for both fresh and FETs. Compared to IVF using partner sperm, this study involved the use of donor sperm, and the majority of patients were healthy women. Whether through fresh ET or FET, the miscarriage rates were lower. This indicates that favourable pelvic conditions may help reduce the incidence of miscarriage.

According to research, the live birth rate was greater in the group receiving FET than in the group receiving fresh ET in the population as a whole (61.5% versus 39.8%; p <0.05).¹³ The live birth rate was considerably greater in women who received frozen embryos than in women who received fresh embryos in a recent multicentre randomised experiment (49% versus 42%; p <0.05).¹⁴ Additionally, it has been asserted that embryo transfers using fresh or frozen-thawed embryos result in similar live delivery rates.¹⁵ In this study, the live birth rates differed significantly (34.78% versus 44.84%; p = 0.012) between fresh ET and FET. Not only that, but as compared to children born following fresh ET, the health status of the newborns delivered after FET was comparable to or even superior. Better results for kids born following fertilisation of FET have been shown in more sizable investigations.¹⁶

Regardless of whether D3 embryos, D5 or D6 blastocysts, or subgroups with a transfer embryo number of 1 or greater than 1, were transferred, FET had a higher clinical pregnancy and live birth rate than fresh ET and a lower miscarriage rate. FET has been demonstrated to be superior to fresh ET from a number of angles, including pregnancy rate, live birth rate, and loss rate.

Additionally, the freezing-thawing of embryos depends on the successful cryopreservation of the embryos. The freezing process known as embryo vitrification avoids the production of ice in suspension and turns the sample into a glassy solid without causing any harm to the cells or tissues. According to some earlier research, even with the most advanced technique, there is still a 3% possibility that embryos would sustain harm because of the potential cytotoxicity of highly concentrated cryoprotectants and the potential for contamination through contact with liquid nitrogen.¹⁵ The majority of recent research, however, has demonstrated that the freeze-thaw procedure has no detrimental effects on embryos.¹⁷ In a follow-up study of children born after FET,¹⁸ Wennerholm et al. came to the reassuring conclusion that the vitrification freezing technique did not appear to have any negative impacts on neonatal outcomes and that newborn outcomes after gradual freezing of embryos. According to Richard J Paulson, vitrification freezing seems to harm oocytes and embryos without having any impact on the progeny.¹⁹ According to Zheng et al., frozen embryos have similar implantation potential and quality to fresh embryos and can lead to pregnancy.²⁰ It has also been shown that freezing of donor sperm does not significantly reduce pregnancy rates when used to fertilise oocytes for IVF.²¹ Thus, cryoinjury of sperm and embryos has a negligible effect on clinical pregnancy rates. Furthermore, a research demons-trated that after the cycles with pregnancy-related compli-cations were excluded, neonatal abnormalities including polydactyly / parallel digits, congenital heart disease, and trisomy 13/18/21 were not adversely impacted by vitrification freezing.²²

This study has several limitations. Firstly, it was conducted in a single institution. Additionally, the study focused on patients from a specific geographical location. This restricts the findings' applicability to other people or areas. Furthermore, the sample size of this study was small, and further data are needed to design a clear protocol.

CONCLUSION

Comprehensive data from this study showed that in 1,065 sperm-donor IVF couples, frozen-thawed embryos had high clinical pregnancy and live birth rates, and when 1 embryo was transferred, the clinical pregnancy and live birth rates were high. Therefore, this research proposes that couples using sperm-donor in-vitro-assisted reproductive technologies and a single FET approach may experience more favourable clinical pregnancy outcomes and obstetric outcomes.

ETHICAL APPROVAL:
Ethical approval for this study was granted by the Bioethics Committee of the Hospital of Reproductive Medicine Centre, Children’s Hospital of Shanxi and Women Health Centre of Shanxi, Affiliated Hospital of Shanxi Medical University, Taiyuan, China and Women Health Centre (IRB-WZ-2024-013).

PATIENTS’ CONSENT:
All data in this article have been obtained with the informed consent of all patients.

COMPETING INTEREST:
The authors declared no conflict of interest.

AUTHORS’ CONTRIBUTION:
JC: Conceptualisation, data curation, investigation, metho-dology, and writing of the original draft.
ZZ: Manuscript editing.
WS, QY, SW: Data collection and management.
XW: Reviewing and editing.
All authors approved the final version of the manuscript to be published.

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