Prediction of embryo survival and live birth rates after cryotransfers of vitrified blastocysts

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.

A 12-h Difference in Exogenous Progesterone Initiation Does Not Have an Impact on Ongoing Pregnancy Rates in Artificial Cycles, as Long as Luteal Phase Support Starts Five Days Before Blastocyst Transfer

PURPOSE

To elucidate if morning or evening start of exogenous progesterone (P4) five days before blastocyst embryo transfer (ET) impacts ongoing pregnancy rates (OPR) in artificial cycles.

METHODS

Single-centre retrospective cohort study of 6493 artificial cycles for an ET (oestrogens and luteal phase support [LPS] with micronized vaginal progesterone [MVP] 400 mg/12 h), conducted at an infertility clinic, December 2018-July 2022. LPS was given from five days before ET. Until March 2021, LPS was started in the evening of day 0 of P4 exposure ("evening start"); since April 2021, LPS was started in the morning of day 0 ("morning start").

RESULTS

Morning start of LPS (n = 2482 cycles); evening start (n = 3983 cycles). Morning or evening start did not exert any impact in OPR (46.9% vs. 46.3%, p = 0.682), as well as after adjusting for any potential confounders (aOR (95%CI): 1.00 (0.89-1.13); p = 0.996). Regarding serum P4 levels, no differences were found between morning (13.4 ± 5.8 ng/ml) and evening start of LPS (13.2 ± 6.4 ng/ml; p = 0.181). However, suboptimal serum P4 levels on the ET day (< 8.8 ng/ml) were registered in 16.6% (n = 411) vs. 19.8% (n = 788) of cycles with a morning and evening start, respectively (p = 0.001).

CONCLUSIONS

A 12-h difference in exogenous P4 initiation does not exert an impact on pregnancy outcomes in artificial cycles with MVP, as far as it is started five days before ET. Results from this study offer a great advantage in patient management, by being able to start LPS either in the morning or in the evening five days before blastocyst transfer.

Testing an artificial intelligence algorithm to predict fetal heartbeat of vitrified-warmed blastocysts from a single image: predictive ability in different settings

STUDY QUESTION

Could an artificial intelligence (AI) algorithm predict fetal heartbeat from images of vitrified-warmed embryos?

SUMMARY ANSWER

Applying AI to vitrified-warmed blastocysts may help predict which ones will result in implantation failure early enough to thaw another.

WHAT IS KNOWN ALREADY

The application of AI in the field of embryology has already proven effective in assessing the quality of fresh embryos. Therefore, it could also be useful to predict the outcome of frozen embryo transfers, some of which do not recover their pre-vitrification volume, collapse, or degenerate after warming without prior evidence.

STUDY DESIGN, SIZE, DURATION

This retrospective cohort study included 1109 embryos from 792 patients. Of these, 568 were vitrified blastocysts cultured in time-lapse systems in the period between warming and transfer, from February 2022 to July 2023. The other 541 were fresh-transferred blastocysts serving as controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Four types of time-lapse images were collected: last frame of development of 541 fresh-transferred blastocysts (FTi), last frame of 467 blastocysts to be vitrified (PVi), first frame post-warming of 568 vitrified embryos (PW1i), and last frame post-warming of 568 vitrified embryos (PW2i). After providing the images to the AI algorithm, the returned scores were compared with the conventional morphology and fetal heartbeat outcomes of the transferred embryos (n = 1098). The contribution of the AI score to fetal heartbeat was analyzed by multivariate logistic regression in different patient populations, and the predictive ability of the models was measured by calculating the area under the receiver-operating characteristic curve (ROC-AUC).

MAIN RESULTS AND THE ROLE OF CHANCE

Fetal heartbeat rate was related to AI score from FTi (P < 0.001), PW1i (P < 0.05), and PW2i (P < 0.001) images. The contribution of AI score to fetal heartbeat was significant in the oocyte donation program for PW2i (odds ratio (OR)=1.13; 95% CI [1.04-1.23]; P < 0.01), and in cycles with autologous oocytes for PW1i (OR = 1.18; 95% CI [1.01-1.38]; P < 0.05) and PW2i (OR = 1.15; 95% CI [1.02-1.30]; P < 0.05), but was not significantly associated with fetal heartbeat in genetically analyzed embryos. AI scores from the four groups of images varied according to morphological category (P < 0.001). The PW2i score differed in collapsed, non-re-expanded, or non-viable embryos compared to normal/viable embryos (P < 0.001). The predictability of the AI score was optimal at a post-warming incubation time of 3.3-4 h (AUC = 0.673).

LIMITATIONS, REASONS FOR CAUTION

The algorithm was designed to assess fresh embryos prior to vitrification, but not thawed ones, so this study should be considered an external trial.

WIDER IMPLICATIONS OF THE FINDINGS

The application of predictive software in the management of frozen embryo transfers may be a useful tool for embryologists, reducing the cancellation rates of cycles in which the blastocyst does not recover from vitrification. Specifically, the algorithm tested in this research could be used to evaluate thawed embryos both in clinics with time-lapse systems and in those with conventional incubators only, as just a single photo is required.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by the Regional Ministry of Innovation, Universities, Science and Digital Society of the Valencian Community (CIACIF/2021/019) and by Instituto de Salud Carlos III (PI21/00283), and co-funded by European Union (ERDF, 'A way to make Europe'). M.M. received personal fees in the last 5 years as honoraria for lectures from Merck, Vitrolife, MSD, Ferring, AIVF, Theramex, Gedeon Richter, Genea Biomedx, and Life Whisperer. There are no other competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Trophectoderm grade is associated with the risk of placenta previa in frozen-thawed single-blastocyst transfer cycles

STUDY QUESTION

Do obstetric and perinatal complications vary according to different blastocyst developmental parameters after frozen-thawed single-blastocyst transfer (SBT) cycles?

SUMMARY ANSWER

Pregnancies following the transfer of a blastocyst with a grade C trophectoderm (TE) were associated with an increased risk of placenta previa compared to those with a blastocyst of grade A TE.

WHAT IS KNOWN ALREADY

Existing studies investigating the effect of blastocyst morphology grades on birth outcomes have mostly focused on fetal growth and have produced conflicting results, while the risk of obstetric complications has rarely been reported. Additionally, growing evidence has suggested that the appearance of TE cells could serve as the most important parameter for predicting implantation and live birth. Given that the TE ultimately develops into the placenta, it is plausible that this independent predictor may also impact placentation.

STUDY DESIGN, SIZE, DURATION

This retrospective cohort study at a tertiary-care academic medical center included 6018 singleton deliveries after frozen-thawed SBT cycles between January 2017 and December 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Singleton pregnancies were grouped into two groups according to blastocyst developmental stage (Days 5 and 6), four groups according to embryo expansion (Stages 3, 4, 5, and 6), three groups according to inner cell mass (ICM) quality (A, B, and C), and three groups according to TE quality (A, B, and C). The main outcomes included pregnancy-induced hypertension, preeclampsia, gestational diabetes mellitus, preterm premature rupture of membrane, placenta previa, placental abruption, placenta accreta, postpartum hemorrhage, preterm birth, low birth weight, small for gestational age, and birth defects. Multivariate logistic regressions were performed to evaluate the effect of blastocyst developmental stage, embryo expansion stage, ICM grade, and TE grade on measured outcomes adjusting for potential confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

No association was found between blastocyst developmental stage and obstetric or perinatal outcomes both before and after adjusting for potential confounders, and similar results were found with regard to embryo expansion stage and ICM grade. Meanwhile, the incidence of placenta previa derived from a blastocyst with TE of grade C was higher compared with those derived from a blastocyst with TE of grade A (1.7%, 2.4%, and 4.0% for A, B, and C, respectively, P = 0.001 for all comparisons). After adjusting for potential covariates, TE grade C blastocysts had 2.81 times the likelihood of resulting in placenta previa compared to TE grade A blastocysts (adjusted odds ratio 2.81, 95% CI 1.11-7.09). No statistically significant differences were detected between any other measured outcomes and TE grades both before or after adjustment.

LIMITATIONS, REASONS FOR CAUTION

The study is limited by its retrospective, single-center design. Additionally, although the sample size was relatively large for the study group, the sample size for certain subgroups was relatively small and lacked adequate power, particularly the ICM grade C group. Therefore, these results should be interpreted with caution.

WIDER IMPLICATIONS OF THE FINDINGS

The study extends our knowledge of the potential downstream effect of TE grade on placental abnormalities.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key Research and Development Program of China (2023YFC2705500, 2023YFC2705501, 2023YFC2705505, 2019YFA0802604); National Natural Science Foundation of China (82130046, 82320108009, 82371660, 32300710); Shanghai leading talent program, Innovative research team of high-level local universities in Shanghai (SHSMU-ZLCX20210201, SHSMU-ZLCX20210200, SHSMU-ZLCX20180401), Shanghai Jiaotong University School of Medicine Affiliated Renji Hospital Clinical Research Innovation Cultivation Fund Program (RJPY-DZX-003), Science and Technology Commission of Shanghai Municipality (23Y11901400), Shanghai's Top Priority Research Center Construction Project (2023ZZ02002), and Three-Year Action Plan for Strengthening the Construction of the Public Health System in Shanghai (GWVI-11.1-36). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Developing and validating a prediction model of live birth following single vitrified-warmed blastocyst transfer

RESEARCH QUESTION

Can the developed clinical prediction model offer an accurate estimate of the likelihood of live birth, involving blastocyst morphology and vitrification day after single vitrified-warmed blastocyst transfer (SVBT), and therefore assist clinicians and patients?

STUDY DESIGN

Retrospective cohort study conducted at a Spanish university-based reproductive medicine unit (2017-2021) including consecutive vitrified-warmed blastocysts from IVF cycles. A multivariable logistic regression incorporated key live birth predictors: vitrification day, embryo score, embryo ploidy status and clinically relevant variables, i.e. maternal age.

RESULTS

The training set involved 1653 SVBT cycles carried out between 2017 and 2020; 592 SVBT cycles from 2021 constituted the external validation dataset. The model revealed that female age and embryo characteristics, including overall quality and blastulation day, is linked to live birth rate in SVBT cycles. Stratification by vitrification day and quality (from day-5A to day-6 C blastocysts) applied to genetically tested and untested embryos. The model's area under the curve was 0.66 (95% CI 0.64 to 0.69) during development and 0.65 (95% CI 0.61 to 0.70) in validation, denoting moderate discrimination. Calibration plots showed strong agreement between predicted and observed probabilities.

CONCLUSION

By incorporating essential predictors such as vitrification day, embryo morphology grade, age and preimplantation genetic testing for aneuploidy usage, this predictive model offers valuable guidance to clinicians and patients, enabling accurate forecasts of live birth rates for any given vitrified blastocyst within SVBT cycles. Additionally, it serves as a potentially indispensable laboratory tool, aiding in selecting the most promising blastocysts for optimal outcomes.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

Should embryo rebiopsy be considered a regular strategy to increase the number of embryos available for transfer?

PURPOSE

To investigate whether embryo rebiopsy increases the yield of in vitro fertilization (IVF) cycles.

METHODS

Retrospective study including 18,028 blastocysts submitted for trophectoderm biopsy and preimplantation genetic testing for aneuploidy (PGT-A) between January 2016 and December 2021 in a private IVF center. Out of the 517 embryos categorized as inconclusive, 400 survived intact to the warming procedure, re-expanded, and were suitable for rebiopsy. Of them, 71 rebiopsied blastocysts were transferred. Factors affecting the probability of obtaining an undiagnosed blastocyst and clinical outcomes from blastocysts biopsied once and twice were investigated.

RESULTS

The overall diagnostic rate was 97.1%, with 517 blastocysts receiving inconclusive reports. Several blastocyst and laboratory features, such as the day of the biopsy, the stage of development, and the biopsy methodology, were related to the risk of obtaining an inconclusive diagnosis after PGT-A. A successful diagnosis was obtained in 384 of the rebiopsied blastocysts, 238 of which were chromosomally transferable. A total of 71 rebiopsied blastocysts were transferred, resulting in 32 clinical pregnancies [(clinical pregnancy rate (CPR)=45.1%], 16 miscarriages [(miscarriage rate (MR)=41%], and, until September 2020, 12 live births [(live birth rate (LBR)=23.1%]. A significantly lower LBR and higher MR were obtained after transferring rebiopsied blastocysts compared to those biopsied once.

CONCLUSION

Although an extra round of biopsy and vitrification may cause a detrimental effect on embryo viability, re-analyzing the test-failure blastocysts contributes to increasing the number of euploid blastocysts available for transfer and the LBR.

Quality assurance (QA) for monitoring the performance of assisted reproductive technology (ART) staff using artificial intelligence (AI)

PURPOSE

Deep learning neural networks have been used to predict the developmental fate and implantation potential of embryos with high accuracy. Such networks have been used as an assistive quality assurance (QA) tool to identify perturbations in the embryo culture environment which may impact clinical outcomes. The present study aimed to evaluate the utility of an AI-QA tool to consistently monitor ART staff performance (MD and embryologist) in embryo transfer (ET), embryo vitrification (EV), embryo warming (EW), and trophectoderm biopsy (TBx).

METHODS

Pregnancy outcomes from groups of 20 consecutive elective single day 5 blastocyst transfers were evaluated for the following procedures: MD performed ET (N = 160 transfers), embryologist performed ET (N = 160 transfers), embryologist performed EV (N = 160 vitrification procedures), embryologist performed EW (N = 160 warming procedures), and embryologist performed TBx (N = 120 biopsies). AI-generated implantation probabilities for the same embryo cohorts were estimated, as were mean AI-predicted and actual implantation rates for each provider and compared using Wilcoxon singed-rank test.

RESULTS

Actual implantation rates following ET performed by one MD provider: "H" was significantly lower than AI-predicted (20% vs. 61%, p = 0.001). Similar results were observed for one embryologist, "H" (30% vs. 60%, p = 0.011). Embryos thawed by embryologist "H" had lower implantation rates compared to AI prediction (25% vs. 60%, p = 0.004). There were no significant differences between actual and AI-predicted implantation rates for EV, TBx, or for the rest of the clinical staff performing ET or EW.

CONCLUSIONS

AI-based QA tools could provide accurate, reproducible, and efficient staff performance monitoring in an ART practice.

The role of timing in frozen embryo transfer

The process of implantation is characterized by a complex cross-talk between the endometrium and the blastocyst, with the endometrium only being receptive to implantation during a transient window of implantation of approximately 2-3 days during the midsecretory phase. The timing of embryo transfer, including frozen embryo transfer, is therefore critical to the success of implantation. In this article, we discuss various elements that may guide the timing of frozen embryo transfer, including the role of endometrial characteristics such as thickness, days postovulation or length of progesterone administration, stage of the embryo, and the application of endometrial receptivity tests to guide personalized embryo transfer.

Individualized luteal phase support normalizes live birth rate in women with low progesterone levels on the day of embryo transfer in artificial endometrial preparation cycles

OBJECTIVE

To analyze the impact on live birth rates (LBRs) of the individualized luteal phase support (termed iLPS) in patients with low serum progesterone (P) levels compared with patients without iLPS.

DESIGN

Retrospective cohort study, December 1, 2018, to May 30, 2019.

SETTING

Private medical center.

PATIENT(S)

A total of 2,275 patients checked for serum P on the day of blastocyst transfer were analyzed. During the study period, 1,299 patients showed serum P levels of ≥9.2 ng/mL, whereas 550 showed serum P levels of <9.2 ng/mL and received iLPS. Additionally, a historical group of 426 patients with serum P levels of <9.2 ng/mL but no iLPS were used for comparison. Eligible patients were aged ≤50 years with adequate endometrium morphology after receiving estrogens. Luteal phase support was provided with micronized vaginal P (MVP) to all women. Patients with personalized initiation of exogenous P according to the endometrial receptivity assay test, polyps, fibroids distorting the cavity, or hydrosalpinx were not included in the analysis.

INTERVENTION(S)

As routine practice since December 2018, patients with low serum P levels received an iLPS with a daily injection of 25 mg of subcutaneous P from the day of embryo transfer (ET) in addition to standard LPS (400 mg of MVP twice a day).

MAIN OUTCOME MEASURE(S)

Live birth rate.

RESULT(S)

The LBR was 44.9% in the iLPS cases vs. 45.0% in patients with normal serum P levels (crude odds ratio [OR], 1.0; 95% confidence interval [CI], 0.82-1.22). By regression analysis, low serum P levels did not affect the LBR after adjusting for possible confounders (age, oocyte origin, fresh vs. frozen, day of ET, embryo quality, number of embryos transferred) (adjusted OR, 0.99; 95% CI, 0.79-1.25). Similarly, no differences were observed in other pregnancy outcomes between groups. The LBR was significantly higher in the group of patients who received additional subcutaneous P (iLPS) compared with the historical group with low serum P levels and no iLPS (44.9% vs. 37.3%; OR, 1.37; 95% CI, 1.06-1.78). In the overall population, patients showing P levels of <9.2 ng/mL on the day of ET were slightly younger and had higher body mass index and lower estradiol and P levels during the proliferative phase compared with patients with P levels of ≥9.2 ng/mL. No differences were observed with regard to the time in between the last dose of MVP and the serum P determination. After a multivariable logistic regression analysis, only body mass index and estradiol levels in the proliferative phase reminded statistically significant. Significant differences in the LBR were observed between patients with serum P levels of <9.2 ng/mL without iLPS and patients with serum P levels of ≥9.2 ng/mL when using either own or donated oocytes.

CONCLUSION(S)

Individualized LPS for patients with low serum P levels produces LBRs similar to those of patients with adequate serum P levels.

Euploid day 7 blastocysts of infertility patients with only slow embryo development have reduced implantation potential

RESEARCH QUESTION

What is the reproductive potential of embryos that achieve blastulation on day 7 followed by preimplantation genetic testing for aneuploidies (PGT-A) for infertility patients with slow embryo development?

DESIGN

This was a retrospective cohort study in a private IVF clinic of consecutive female infertility patients (n = 2966) aged 24-48 (36.3 ± 3.8) years who underwent frozen embryo transfer (FET) of a single euploid blastocyst.

RESULTS

The women underwent single euploid FET of an embryo that achieved blastulation on day 5 (n = 1880), day 6 (n = 986) or day 7 (n = 100). Day 7 embryos resulted in lower implantation and live birth rates compared with both day 5 and day 6 embryos (P < 0.001). The day 5, day 6 and day 7 groups had 68.5%, 55.2% and 36.0% live birth rates, respectively. The day 7 group was older than the day 5 group (P < 0.001); comparing age-matched cohorts, the day 7 group still had lower implantation and live birth rates (P < 0.0001 and P < 0.001, respectively). Embryo grade was unrelated to live birth rates. Day 7 embryos of expansion grade 5 or 6 or trophectoderm grade A were more likely to be euploid compared with expansion grade 3 or trophectoderm grade B.

CONCLUSIONS

Euploid day 7 embryos represented reduced implantation potential, even when controlling for maternal age. Of all day 7 embryos that underwent PGT-A, euploidy was associated with expansion grade 5 or 6 and trophectoderm grade A. These results can help providers manage patient expectations in cases where infertile women have slow embryo development.