Effectiveness and Safety of Two Consecutive Cycles of Single Embryo Transfer Compared With One Cycle of Double Embryo Transfer: A Systematic Review and Meta-Analysis

Effectiveness and safety of consecutive single embryo transfer compared to double embryo transfer: results from the UK HFEA registry

STUDY QUESTION

How does two-consecutive single embryo transfer (2xSET) affect reproductive outcomes of IVF and ICSI compared to double embryo transfer (DET)?

SUMMARY ANSWER

Two-consecutive SET may provide greater or comparable live birth rate (LBR); with lower multiple birth, preterm birth, and pregnancy loss or neonatal death rates compared to DET.

WHAT IS KNOWN ALREADY

Elective SET in IVF/ICSI is widely encouraged over DET to minimize the risk of multiple births and associated morbidities. Despite this, multiple birth rates following IVF remain higher than the 10% target across Europe and the USA. Currently, the majority of evidence regarding SET and DET is based on various studies assessing outcomes such as LBR per treatment cycle, as opposed to per oocyte retrieval. As such, the representation of SET is mostly unfavourable. Analysis of cumulative LBR following the transfer of two embryos over consecutive cycles, rather than in one transfer event (DET) is more effective at distinguishing the two methods and will therefore provide more valuable information relevant to clinical practice.

STUDY DESIGN, SIZE, DURATION

This retrospective cohort study was conducted using Human Fertilisation and Embryology Authority (HFEA) register data, which encompasses national data from all IVF clinics in the UK. All women who underwent their first oocyte retrieval and IVF or ICSI treatment cycle with subsequent SET, DET, or 2xSET between 2010 and 2019 using blastocyst embryos were included (N = 71 807).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The rate of live birth, liveborn baby rate, multiple birth, preterm birth, and pregnancy loss or neonatal death was compared between SET, DET, and 2xSET IVF/ICSI pregnancies using blastocyst-stage embryos, where data were stratified by maternal age. Data analysis was conducted in RStudio v4.2, alpha equals 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Blastocyst-stage 2xSET achieved a greater median LBR of 0.47 (interquartile range [IQR] 0.13) than SET, 0.41 (IQR 0.13), and DET, 0.38 (IQR 0.13) (P < 0.05). Using SET as the reference standard, 2xSET was associated with a significantly lower odds of multiple births compared to DET ((odds ratio [OR] 6.87, 95% CI 6.14-7.68) vs 28.20, 95% CI 25.20-31.57). The odds of preterm birth were also lower following 2xSET (OR 1.11, 95% CI 1.06-1.15) compared to DET (OR 2.80, 95% CI 2.67-2.94). Similarly, the odds of pregnancy loss or neonatal death were lower following 2xSET (OR 1.14, 95% CI 1.08-1.21) compared to DET (OR 2.11, 95% CI 1.98-2.24). LBR was consistently higher following 2xSET than DET and SET in women aged 39 years and under (P < 0.05). However, results were comparable in women over 39 years (P > 0.05). Across all age groups, DET pregnancies had the highest multiple birth rate (P < 0.05). In women aged 39 years and under, DET was associated with the highest preterm birth rate (P < 0.05), whereas the rate was comparable across cohorts in women over 39 (P > 0.05). Moreover, pregnancy loss and neonatal death rates were highest following DET in women aged 37 years and under (P < 0.05), and comparable to SET and 2xSET in women over 37 years (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION

Certain confounders are not recorded within HFEA registry data, including patient BMI, evaluation of embryo quality, and endometrial thickness at embryo transfer. Consequently, while our analysis identifies broad trends in embryo transfer success and morbidity, results may differ within certain patient populations.

WIDER IMPLICATIONS OF THE FINDINGS

Blastocyst-stage 2xSET may provide greater LBR in women aged 39 years and under, and comparable LBR in women over 39 years old, with overall lower multiple birth and morbidity than DET. 2xSET should be considered first-line among certain patient cohorts, including women with advanced maternal age to improve reproductive outcomes and reduce the risk of morbidity following ART.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used for this study. None of the authors has any conflicts of interest.

TRIAL REGISTRATION NUMBER

This cohort study did not require registration. Following consultation with the Institutional Review Board at Imperial College London, ethical approval was not deemed necessary.

One fresh cleavage-stage single embryo transfer (SET) plus one frozen-thawed blastocyst-stage SET or one fresh cleavage-stage double embryo transfer? A retrospective matched cohort study

STUDY QUESTION

Are there significant differences in fertility outcomes between transferring two cleavage-stage embryos in a single fresh cycle and transferring one cleavage-stage embryo in a fresh cycle and one blastocyst-stage embryo in the subsequent frozen-thawed cycle?

SUMMARY ANSWER

In women aged <38 years with two embryos available, transferring one cleavage-stage embryo in a fresh cycle and one blastocyst-stage embryo in the subsequent frozen-thawed cycle increased live birth rates and decreased multiple live birth rates compared to transferring two cleavage-stage embryos in a single fresh cycle.

WHAT IS KNOWN ALREADY

The strategy of repeated single embryo transfer (SET) has emerged as a solution to address the reduced live birth rates associated with SET per cycle. There is substantial evidence indicating that the cumulative live birth rate after repeated SET is comparable to that of double embryo transfer (DET), while significantly reducing the incidence of multiple pregnancies. Evidence regarding the outcomes of transferring two cleavage-stage embryos in a single fresh cycle versus transferring one cleavage-stage embryo in one fresh cycle and one blastocyst-stage embryo in the subsequent frozen-thawed cycle is scarce.

STUDY DESIGN, SIZE, DURATION

This study is a retrospective matched cohort study, where data were gathered from the clinical database of women who underwent IVF treatment at the Reproductive Center of Peking University Third Hospital between January 2011 and December 2019, with follow-up extending until December 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study group included cycles with a fresh cleavage-stage SET and a subsequent frozen-thawed blastocyst-stage SET (2xSET, N = 976). Fresh cleavage-stage DET was the control group (DET, N = 976). Included cycles were divided into subgroups based on age (≥38 years vs <38 years) and total number of utilizable (transferred or cryopreserved) embryos (=2 vs >2).

MAIN RESULTS AND THE ROLE OF CHANCE

The duration of infertility, prevalence of unexplained infertility, and controlled ovarian stimulation regimes differed significantly between the two groups and were adjusted for in the further analysis. We observed a significant increase in clinical pregnancies (55.5% vs 42%, adjusted odds ratio (OR) 1.87 [1.55-2.26]) and live births (44.8% vs 34.5%, adjusted OR 1.63 [1.35-1.97]) in favor of the 2xSET group. The preterm birth rate was lower in the study group (adjusted OR 0.64 [0.42-0.96]). Neonatal birth weight of singletons was similar between the two groups (adjusted B 4.94 g [-84.5 to 94.4]). The beneficial effect on the live birth rate disappeared in cases where aged 38 years and older or when only two embryos were utilizable.

LIMITATIONS, REASONS FOR CAUTION

This study is limited by differences in baseline characteristics of the two groups. Analyzing two consecutive SETs at the cleavage stage was not feasible. Additionally, the homogeneous population limits generalizability to other ethnic groups, which should be considered when interpreting the results broadly.

WIDER IMPLICATIONS OF THE FINDINGS

We recommend a combination strategy for women under 38 years old and with more than two embryos available: transfer one cleavage-stage embryo in the fresh cycle, followed by one blastocyst-stage embryo in the subsequent frozen-thawed cycle. This strategy reduces the risk of blastocyst culture failure while maintaining a high success rate. It offers hope to families seeking additional children and avoids unnecessary embryo disposal.

STUDY FUNDING/COMPETING INTEREST(S)

B.W.M. had received grants from NHMRC, Ferring, Merck, and Guerbet, consulting fees and stock options from ObsEva, is on the advisory board of ObsEva, and reports consultancy for Guerbet, none of which are in relation to the present manuscript. All other authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Determining Factors Influencing The Successful Embryo Transfer and Pregnancy during The Frozen Cycle of In Vitro Fertilization: A Retrospective Cohort Study

BACKGROUND

Frozen embryo transfer (FET) has been increasingly used due to advancements in cryopreservation techniques and the safety advantages. This study aims to determine various factors influencing the successful FET.

MATERIALS AND METHODS

Retrospective cohort analysis included 1112 women who underwent programmed FET between January 2012 and October 2022, at King Chulalongkorn Memorial Hospital, Thailand. Patient characteristics, embryo characteristics, endometrial preparation protocol, endometrial characteristics (thickness, pattern), embryo transfer procedure (tip and flow during transfer, embryo placement location, the difficulty of the procedure, presence of blood and mucous at catheter), and operator factor were analyzed. Multiple logistic regression analysis was used to assess the relationship between collected variables and successful embryo transfer which is defined by clinical pregnancy.

RESULTS

The overall clinical pregnancy rate was 34.2%. Women aged 35-40 years and >40 years were less likely to have a clinical pregnancy compared to those aged <35 years [adjusted odds ratio (aOR): 0.523; 95% confidence intervals (CI): 0.360-0.757, P<0.001 and aOR: 0.260; 95% CI: 0.152-0.434, P<0.001, respectively]. Obese women with body mass index (BMI) ≥25 kg/m2 were significantly associated with decreased clinical pregnancy (aOR: 0.632; 95% CI: 0.403-0.978, P=0.042) compared to those with normal BMI. Day-3 and day-4 embryo transfer showed a significant decrease in clinical pregnancy compared to blastocyst transfer (aOR: 0.294; 95% CI: 0.173-0.485, P<0.001 and aOR: 0.497; 95% CI: 0.265-0.900, P=0.024). Double embryo transfer (DET) was 1.78 times more likely to have a clinical pregnancy than women with single embryo transfer (SET) (aOR: 1.779; 95% CI: 1.293-2.458, P<0.001). The cycles with endometrial thickness <8 mm were associated with a decrease in clinical pregnancy compared with those with a thickness ≥8 mm (aOR: 0.443; 95% CI: 0.225-0.823, P=0.013).

CONCLUSION

Older age, obesity, non-blastocyst transfer, single embryo transfer, and endometrial thickness of <8 mm were significantly associated with a decreased clinical pregnancy in programmed FET.

Determining Factors Affecting the Successful Outcome of Fresh Embryo Transfer During In Vitro Fertilization: A Retrospective Cohort Study

Background

Fresh embryo transfer has been decreasing because of advancements in vitrification techniques and safety concerns related to ovarian hyperresponse. However, in normal responders, clinical outcomes appear to be comparable with those with frozen embryo transfer. This study aimed to determine factors that influence successful fresh embryo transfer.

Methods

This retrospective cohort study included 521 women who underwent in vitro fertilization (IVF) and fresh embryo transfer at King Chulalongkorn Memorial Hospital, Thailand. Patients' clinical data, embryo details, endometrial characteristics (thickness and pattern), and embryo transfer procedures (tip and flow during transfer, embryo placement location, difficulty of the procedure, and presence of blood and mucous at catheter) were analyzed. Chi-square test, Fisher's exact test, Student's t-test, and logistic regression were performed for data analysis. A p-value of <0.05 was considered statistically significant.

Results

The overall clinical pregnancy rate was 17.1%. Women aged >40 years were less likely to have a clinical pregnancy than those aged <35 years (adjusted odds ratio [aOR] 0.422; 95% confidence intervals [CI] 0.196-0.908, p=0.027). Day 3 embryo transfer showed a significant decrease in clinical pregnancy compared with blastocyst transfer (aOR 0.514; 95%CI 0.287-0.923, p=0.026). In the subgroup analysis for blastocyst transfer, women with good-quality blastocyst (≥322) were 2.439 times more likely to have a clinical pregnancy than those with poor-quality blastocysts (aOR 2.439; 95%CI 1.199-4.962, p=0.014).

Conclusion

Advanced age and day 3 embryo transfer were significantly associated with low clinical pregnancy rates in fresh embryo transfer.

Effect of post-vitrification cryopreservation duration on singleton birth-weight in frozen-thawed blastocysts transfer cycles

Introduction

This study aimed to explore the effect of cryopreservation duration after blastocyst vitrification on the singleton birth-weight of newborns to assess the safety of long-term preservation of frozen-thawed blastocyst transfer (FBT) cycles.

Methods

This was a retrospective observational study conducted at the Gynecological Endocrinology and Assisted Reproduction Center of the Peking Union Medical College Hospital. Patients who gave birth to singletons between January 2006 and December 2021 after undergoing FBT cycles were included. Five groups were formed according to the duration of cryopreservation of embryos at FBT: Group I included 274 patients with a storage time < 3 months. Group II included 607 patients with a storage time of 3-6 months. Group III included 322 patients with a storage time of 6-12 months. Group IV included 190 patients with a storage time of 12-24 months. Group V included 118 patients with a storage time of > 24 months. Neonatal outcomes were compared among the groups. Multivariate linear regression analysis was performed to evaluate birth-weights and other birth-related outcomes.

Results

A total of 1,511 patients were included in the analysis. The longest cryopreservation period was 12 years. The birth-weights of neonates in the five groups were 3344.1 ± 529.3, 3326.1 ± 565.7, 3260.3 ± 584.1, 3349.9 ± 582.7, and 3296.7 ± 491.9 g, respectively (P > 0.05). The incidences of preterm birth, very preterm birth, low birth-weight, and very low birth-weight were similar in all groups (P > 0.05). The large-for-gestational-age and small-for-gestational-age rates did not differ significantly among the groups (P > 0.05). After adjusting for confounding factors that may affect neonatal outcomes, a trend for an increased risk of low birth-weight with prolonged cryopreservation was observed. However, cryopreservation duration and neonatal birth-weight were not significantly correlated (P > 0.05).

Conclusion

The duration of cryopreservation after blastocyst vitrification with an open device for more than 2 years had no significant effect on the birth-weight of FBT singletons; however, attention should be paid to a possible increase in the risk of low birth-weight.

Management strategies following implantation failure of euploid embryos

Background

Euploid blastocyst implantation failure may result from embryonic factors undetectable by preimplantation genetic testing for aneuploidy (PGT-A); however, various nonembryonic factors can also intricately interfere with implantation. This review seeks to clarify evidence-based testing and treatments for implantation failure after euploid embryo transfer.

Methods

We conducted a review of the literature on implantation failure after euploid embryo transfer or multiple embryo transfer cycles, which mainly included systematic reviews and meta-analyses.

Results

The recommended tests for implantation failure include (1) hysteroscopy, (2) endometrial CD138 immunohistochemistry and bacterial culture, (3) serum 25-hydroxyvitamin D3, and (4) thrombophilia screening. Based on diagnostic findings, the following treatments have been recommended: (1) antibiotics for chronic endometritis, (2) vitamin D replacement, (3) lifestyle modification, and (4) low-dose aspirin starting from the postimplantation period for thrombophilia. Moreover, frozen-thawed single euploid blastocyst transfer using assisted hatching and hyaluronan-enriched transfer medium may support embryo implantation.

Conclusion

To ensure a successful pregnancy in subsequent embryo transfers, simple, inexpensive, and evidence-based tests and treatments should be selected.