Impact of Caesarean section on pregnancy outcomes in ART after transfer of one or more frozen blastocysts.

INTRODUCTION: The prevalence of Caesarean delivery is rising steadily worldwide, and it is important to identify its future impact on fertility. A number of articles have been published on this subject, but the impact of Caesarean section on reproductive outcomes is still under debate, and none of these articles focus exclusively on frozen blastocysts. OBJECTIVE: The aim of this study was to evaluate the impact of a previous Caesarean delivery compared with a previous vaginal delivery on the chances of a live birth following the transfer of one or more frozen embryos at the blastocyst stage. METHODS: This was a retrospective, bicentric study at the University Hospitals of Nîmes and Montpellier, conducted between January 1st, 2016 and February 1st, 2021. Three hundred and ninety women with a history of childbirth and a transfer of one or more frozen embryos at blastocyst stage were included in the analysis. The primary outcome was the number of live births. Secondary outcomes were: the rate of positive HCG, miscarriage, ectopic pregnancy and clinical pregnancy, as well as the live birth rate according to the presence or absence of an isthmocele. RESULTS: Of the 390 patients included, 118 had a previous Caesarean delivery and 272 a vaginal delivery. No statistically significant differences were found for the primary (p = 0.9) or secondary outcomes. A trend towards lower live birth rates was observed in patients with isthmoceles, but this did not reach significance (p>0.9). On the other hand, transfers were more often described as difficult in the Caesarean delivery group (p = 0.011). CONCLUSION: Our study found no effect of previous Caesarean delivery on the chances of live birth after transferring one or more frozen blastocysts. However, further prospective studies are needed to confirm these results.

Serum progesterone concentration on pregnancy test day might predict ongoing pregnancy after controlled ovarian stimulation and fresh embryo transfer.

Progesterone (P4) is essential for pregnancy. A controlled ovarian stimulation (COS) leads to a iatrogenic luteal defect that indicates a luteal phase support (LPS) at least until pregnancy test day. Some clinicians continue the LPS until week 8 or later, when P4 is mainly secreted by syncytiotrophoblast cells.Measuring serum P4 on pregnancy test day after a fresh embryo transfer could help to identify women who might benefit from prolonged LPS. In women with LPS based on P4 administered by the rectal route, P4 concentration on pregnancy test day was significantly higher in patients with ongoing pregnancy than in patients with abnormal pregnancy.This monocentric retrospective study used data on 99 consecutive cycles of COS, triggered with human chorionic gonadotropin, followed by fresh embryo transfer resulting in a positive pregnancy test (>100 IU/L) (from November 2020 to November 2022). Patients undergoing preimplantation genetic screening or with ectopic pregnancy were excluded. All patients received standard luteal phase support (i.e. micronized vaginal progesterone 600 mg per day for 15 days). The primary endpoint was P4 concentration at day 15 after oocyte retrieval (pregnancy test day) in women with ongoing pregnancy for >12 weeks and in patients with miscarriage before week 12 of pregnancy.The median P4 concentration [range] at pregnancy test day was higher in women with ongoing pregnancy than in women with miscarriage (55.9 ng/mL [11.6; 290.6] versus 18.1 ng/mL [8.3; 140.9], p = 0.002). A P4 concentration ≥16.5 ng/mL at pregnancy test day was associated with higher ongoing pregnancy rate (OR = 12.5, 95% CI 3.61 - 43.33, p <0.001). A P4 concentration ≥16.5 ng/mL at pregnancy test day was significantly associated with higher live birth rate (OR = 11.88, 95% CI 3.30-42.71, p <0.001).After COS and fresh embryo transfer, the risk of miscarriage is higher in women who discontinue luteal support after 15 days, as recommended, but with P4 concentration <16.5 ng/mL. The benefit of individualized prolonged luteal phase support should be evaluated.

Cytochalasin D restores nuclear size acting on F-actin and IZUMO1 localization in low-quality spermatozoa.

In spermatozoa, the nuclear F-actin supports the acroplaxome, a subacrosomal structure involved in the correct exposure of several acrosomal membrane proteins; among them, the glycoprotein IZUMO1 is the major protein involved in sperm-oocyte fusion. Nuclear F-actin is also involved in sperm head shaping and chromosome compartmentalization. To date, few notions regarding the bivalent role of F-actin on sperm chromatin organization and IZUMO1 positioning have been reported. In our work, we characterized subcellular organization of F-actin in human high- and low-quality spermatozoa (A- and B-SPZ), respectively, showing that F-actin over-expression in sperm head of B-SPZ affected IZUMO1 localization. A correct IZUMO1 repositioning following in vitro induction of F-actin depolymerization, by cytochalasin D treatment, occurred. Interestingly, F-actin depolymerization was also associated with a correct acrosome repositioning, thus to favor a proper acrosome reaction onset, with changes in sperm nuclear size parameters and histone acetylation rate reaching high-quality conditions. In conclusion, the current work shows a key role of F-actin in the control of IZUMO1 localization as well as chromatin remodeling and acetylation events.

[The impact of oocyte cryopreservation time in oocyte donation on the clinical success rate]. / Impact de la durée de cryoconservation ovocytaire dans le cadre du don d'ovocytes sur le taux de succès clinique.

OBJECTIVES: To evaluate the impact of the cryopreservation time of vitrified oocytes on the success rates in oocyte donation cycles. METHODS: A retrospective study was carried out on 156 cycles with donated oocytes from January 2012 to September 2021. All the cycles were sorted according to the storage time of the oocytes (25 in the group 1:<3 months, 32 in the group 2: between 3 and 6 months, 39 in the group 3: between 6 and 12 months, 38 in the group 4: between 12 and 24 months and 22 in the group 5:>24 months). Clinical outcomes after ART, survival rates at thawing and oocyte fertilization rates were compared between the different cohorts stratified according to oocyte storage duration. A binary multivariate logistic regression was performed adjusting for the identified confounders. RESULTS: Prolonged storage time of vitrified oocytes had an effect on their survival post-thawing rates, but no significant effect was identified on fertilization rates or clinical outcomes. After adjusting for the confounders, the relationships between clinical outcomes and oocytes storage time did not reach statistical significance. Our study was characterized by a limited cohort with data from a single ART center. CONCLUSIONS: Our study doesn't highlight any significant difference in the use of long-stored vitrified oocytes (more than 2 years) on clinical issues in ART. The conclusion of our study needs to be verified in further studies with larger cohorts.

Sperm Meiotic Segregation Analysis of Reciprocal Translocations Carriers: We Have Bigger FISH to Fry.

Reciprocal translocation (RT) carriers produce a proportion of unbalanced gametes that expose them to a higher risk of infertility, recurrent miscarriage, and fetus or children with congenital anomalies and developmental delay. To reduce these risks, RT carriers can benefit from prenatal diagnosis (PND) or preimplantation genetic diagnosis (PGD). Sperm fluorescence in situ hybridization (spermFISH) has been used for decades to investigate the sperm meiotic segregation of RT carriers, but a recent report indicates a very low correlation between spermFISH and PGD outcomes, raising the question of the usefulness of spermFISH for these patients. To address this point, we report here the meiotic segregation of 41 RT carriers, the largest cohort reported to date, and conduct a review of the literature to investigate global segregation rates and look for factors that may or may not influence them. We confirm that the involvement of acrocentric chromosomes in the translocation leads to more unbalanced gamete proportions, in contrast to sperm parameters or patient age. In view of the dispersion of balanced sperm rates, we conclude that routine implementation of spermFISH is not beneficial for RT carriers.

Individualized luteal phase support based on serum progesterone levels in frozen-thawed embryo transfer cycles maximizes reproductive outcomes in a cohort undergoing preimplantation genetic testing.

Introduction: Low serum progesterone concentration on frozen embryo transfer (FET) day in hormone replacement therapy (HRT) cycles results in lower reproductive outcomes. Recent studies showed the efficiency of a "rescue protocol'' to restore reproductive outcomes in these patients. Here, we compared reproductive outcomes in HRT FET cycles in women with low serum progesterone levels who received individualized luteal phase support (iLPS) and in women with adequate serum progesterone levels who underwent in vitro fertilization for pre-implantation genetic testing for structural rearrangements or monogenic disorders. Design: This retrospective cohort study included women (18-43 years of age) undergoing HRT FET cycles with pre-implantation genetic testing at Montpellier University Hospital between June 2020 and May 2022. A standard HRT was used: vaginal micronized estradiol (6mg/day) followed by vaginal micronized progesterone (VMP; 800 mg/day). Serum progesterone was measured after four doses of VMP: if <11ng/ml, 25mg/day subcutaneous progesterone or 30mg/day oral dydrogesterone was introduced. Results: 125 HRT FET cycles were performed in 111 patients. Oral/subcutaneous progesterone supplementation concerned 39 cycles (n=20 with subcutaneous progesterone and n=19 with oral dydrogesterone). Clinical and laboratory parameters of the cycles were comparable between groups. The ongoing pregnancy rate (OPR) was 41.03% in the supplemented group and 18.60% in the non-supplemented group (p= 0.008). The biochemical pregnancy rate and miscarriages rate tended to be higher in the non-supplemented group versus the supplemented group: 13.95% versus 5.13% and 38.46% versus 15.79% (p=0.147 and 0.182 respectively). Multivariate logistic regression analysis found that progesterone supplementation was significantly associated with higher OPR ​​ (adjusted OR = 3.25, 95% CI [1.38 - 7.68], p=0.007). Conclusion: In HRT FET cycles, progesterone supplementation in patients with serum progesterone concentration <11 ng/mL after four doses of VMP significantly increases the OPR.

"Short agonist stop" protocol, an ovarian stimulation for poor responders in in vitro fertilization (IVF): A pilot study.

Introduction: Poor responder patients remain a challenge in assisted reproductive technologies. The "short agonist stop" (SAS) stimulation protocol uses a double stimulation (flare up effect with the gonadotropin-releasing hormone (GnRH) agonist (GnRH-a) then gonadotropins) associated with a less strenuous blockage (discontinuation of GnRH-a) to favor follicular recruitment in order to obtain a better ovarian response. This study aims to compare the number of oocytes obtained after a SAS stimulation protocol with those obtained after the previous stimulation protocol, in the same women, with poor ovarian response (POR) diagnosed according to the POSEIDON criteria. Design: This therapeutic observational retrospective cohort from 2018 to 2022, with a case-control evaluation compared with the same patients' previous performance, included women with POR undergoing IVF with SAS stimulation protocol. The primary outcome was the number of total oocytes recovered and secondary outcomes were the numbers of mature oocytes, total embryos observed at day 2 and usable cleaved embryos and blastocysts (day 5/6). Results: 63 patients with SAS and previous cycles were included. In the SAS group, the mean number of oocytes was significantly higher: 7.3 vs 5.7, p=0.018 in comparison with the previous attempt. So was the number of mature oocytes (5.8 vs 4.1, p=0.032) and the total mean number of embryos obtained at day 2 (4.1 versus 2.7, p=0.016). The SAS stimulation generated 84 usable embryos: 57 cleaved embryos and 27 blastocysts. The mean number of usable embryos was similar in both groups (1.64 vs 1.31, respectively, p=0.178). In total, out of 63 patients, after the SAS protocol, and subsequent embryo transfers (fresh and frozen, n=54), 9 patients had ongoing pregnancies and no miscarriage occurred. The cumulative ongoing pregnancy rate (cOPR) after the SAS protocol was 14.3% (9/63) per oocyte pick-up and 16.7% (9/54) per transfer. Conclusion: SAS stimulation is a short and original protocol strengthening the therapeutic arsenal of poor responders, that may offer promising results for those patients with low prognosis and previous failed IVF. Results must be confirmed with a randomized controlled trial.

Molecular Characterization of a Rare Case of Monozygotic Dichorionic Diamniotic Twin Pregnancy after Single Blastocyst Transfer in Preimplantation Genetic Testing (PGT).

Preimplantation genetic testing (PGT) is widely used to select unaffected embryos, increasing the odds of having a healthy baby. During the last few decades, it was accepted that monozygotic dichorionic diamniotic twin pregnancies occurred from the embryo splitting before Day 3 postfertilization according to Corner's dogma. Hence, the occurrence of a dichorionic diamniotic twin pregnancy after a single blastocyst transfer was considered a dizygotic pregnancy resulting from blastocyst transfer and concurrent natural fertilization. In our study, we have provided for the first time molecular proof that a single blastocyst transfer can result in a monozygotic dichorionic diamniotic twin pregnancy, invalidating Corner's dogma. In this case, we recommend systematically assessing the genetic status of dichorionic twins after single blastocyst transfer using prenatal diagnosis to exclude the risk from a potential concurrent spontaneous pregnancy and to ensure that both fetuses are unaffected. To achieve this goal, we have developed here an innovative noninvasive prenatal diagnosis by exclusion of paternal variants with droplet digital PCR, maximizing the reliability of genetic diagnosis. Further multicentric prospective studies using genetic testing are now required to establish the rate of blastocyst splitting leading to dichorionic pregnancy in PGT and to identify the risk factors.

Fertility preservation in patients of childbearing age treated for breast cancer: A nationwide cohort study.

BACKGROUND: Approximately 7% of breast cancers are diagnosed in women under 40. Question of subsequent fertility has become fundamental. We aimed to evaluate the rate of fertility preservation (FP) by oocyte retrieval (OR) after ovarian stimulation in patients of childbearing age, managed for breast cancer with adjuvant chemotherapy in France, reuse rate of frozen gametes and live births rate (LBR) after treatment. METHODS: We included 15,774 women between 18 and 40 years old, managed by surgery and adjuvant chemotherapy for breast cancer, between January 2011 and December 2020 from a French health registry. Patients with OR after breast surgery and before chemotherapy were considered as FP group; those with no OR as no FP group. To compare LBR with French population independently of age, we calculated Standardized Incidence Rates (SIR) of live births using indirect standardization method. RESULTS: FP rate increased gradually since 2011, reaching 17% in 2019. A decrease in use was observed in 2020 (13,9%). Among patients with at least 2 years of follow-up, gamete reuse rate was 5,6%. Births after cancer were mostly from spontaneous pregnancies. Among patients with at least 3 years of follow-up, LBR was 19,6% in FP group, 3,9% in second group. SIR of live births was of 1,05 (95% CI = 0.91-1.19) and 0.33 (95% CI = 0.30-0.36) in FP and no FP group respectively. CONCLUSION: Oncofertility activity increased until 2019 in France, reaching 17%. Gamete reuse rate was low. Births resulted mainly from spontaneous pregnancies. SIR of live births was lower in no FP group.

[Impact of SARS-CoV-2 on fertility, gametes' quality and Assisted Reproduction Technology]. / Impact du SARS-CoV-2 sur la fertilité, les gamètes et l'Assistance médicale à la procréation.

The current pandemic context raises questions about COVID-19 consequences on Assisted Reproduction Technology (ART). Indeed, according to the first Biomedicine Agency recommendations, ART centers suspended their activities in March 2020 during the first wave of Covid-19. However, SARS-CoV-2 direct and indirect effects on gametes, fertility, pregnancy and neonatal health are still debated. The aim of this review is to assess the available data on this subject, to inform patients in care and adapt daily practice. Most recent studies are based on the effects of the infectious syndrome, on hormonal factors as well as on the expression of viral entry proteins (ACE2 and TMPRSS2) in cells involved in gametogenesis, to assess the impact of COVID-19. So far, no effect on female gametes was highlighted. More studies are needed to confirm this hypothesis. Mother to children transmission couldn't be proven, yet neonatal infection remains possible. However, men are more susceptible to be infected by SARS-CoV-2, to be symptomatic, and spermatogenesis is likely to be affected. Presence of the virus in semen is infrequently reported, but all of these parameters should be taken into account in ART.

Endometrial miRNome profile according to the receptivity status and implantation failure.

This is a retrospective study to evaluate if the miRNome profile of endometrium samples collected during the implantation window predicts Assisted Reproduction Technology (ART) outcomes. We first investigated the endometrial miRNome profile according to the receptivity status in 20 patients with repeated implantation failures (RIF) (discovery cohort). After customized embryo transfer, the miRNome profiles of receptive patients with a positive or negative ß-hCG, and with early miscarriage or live birth were analysed. Some differentially expressed miRNAs were selected for validation by RT-qPCR in endometrial samples from 103 RIF patients (validation cohort). Analysis of the different miRNome profiles identified endometrial receptivity, implantation failure, and early miscarriage-associated miRNA signatures that included 11, 261, and 76 miRNAs, respectively. However, only four miRNAs associated with the endometrial receptivity status (miR-455-3p and miR-4423-3p) and implantation failure (miR-152-3p and miR-155-5p) were significantly validated in endometrial samples. The miRNome profile of endometrial tissues during the implantation window can predict the pregnancy outcome. These data are crucial for opening new perspectives to predict implantation failure and consequently, to increase ART success.

SPART: A versatile and standardized data exchange format for species partition information.

A wide range of data types can be used to delimit species and various computer-based tools dedicated to this task are now available. Although these formalized approaches have significantly contributed to increase the objectivity of species delimitation (SD) under different assumptions, they are not routinely used by alpha-taxonomists. One obvious shortcoming is the lack of interoperability among the various independently developed SD programs. Given the frequent incongruences between species partitions inferred by different SD approaches, researchers applying these methods often seek to compare these alternative species partitions to evaluate the robustness of the species boundaries. This procedure is excessively time consuming at present, and the lack of a standard format for species partitions is a major obstacle. Here, we propose a standardized format, SPART, to enable compatibility between different SD tools exporting or importing partitions. This format reports the partitions and describes, for each of them, the assignment of individuals to the "inferred species". The syntax also allows support values to be optionally reported, as well as original trees and the full command lines used in the respective SD analyses. Two variants of this format are proposed, overall using the same terminology but presenting the data either optimized for human readability (matricial SPART) or in a format in which each partition forms a separate block (SPART.XML). ABGD, DELINEATE, GMYC, PTP and TR2 have already been adapted to output SPART files and a new version of LIMES has been developed to import, export, merge and split them.

SARS-CoV-2 and Implantation Window: Gene Expression Mapping of Human Endometrium and Preimplantation Embryo.

Understanding whether SARS-CoV-2 could infect cells and tissues handled during ART is crucial for risk mitigation, especially during the implantation window when either endometrial biopsies are often practiced for endometrial receptivity assessment or embryo transfer is performed. To address this question, this review analyzed current knowledge of the field and retrospectively examined the gene expression profiles of SARS-CoV-2-associated receptors and proteases in a cohort of ART candidates using our previous Affymetrix microarray data. Human endometrial tissue under natural and controlled ovarian stimulation cycles and preimplantation embryos were analyzed. A focus was particularly drawn on the renin-angiotensin system, which plays a prominent role in the virus infection, and we compared the gene expression levels of receptors and proteases related to SARS-CoV-2 infection in the samples. High prevalence of genes related to the ACE2 pathway during both cycle phases and mainly during the mid-secretory phase for ACE2 were reported. The impact of COS protocols on endometrial gene expression profile of SARS-CoV-2-associated receptors and proteases is minimal, suggesting no additional potential risks during stimulated ART procedure. In blastocysts, ACE2, BSG, CTSL, CTSA and FURIN were detectable in the entire cohort at high expression level. Specimens from female genital tract should be considered as potential targets for SARS-CoV-2, especially during the implantation window.

Biphasic (5-2%) oxygen concentration strategy significantly improves the usable blastocyst and cumulative live birth rates in in vitro fertilization.

Oxygen (O2) concentration is approximately 5% in the fallopian tube and 2% in the uterus in humans. A "back to nature" approach could increase in vitro fertilization (IVF) outcomes. This hypothesis was tested in this monocentric observational retrospective study that included 120 couples who underwent two IVF cycles between 2014 and 2019. Embryos were cultured at 5% from day 0 (D0) to D5/6 (monophasic O2 concentration strategy) in the first IVF cycle, and at 5% O2 from D0 to D3 and 2% O2 from D3 to D5/6 (biphasic O2 concentration strategy) in the second IVF cycle. The total and usable blastocyst rates (44.4% vs. 54.8%, p = 0.049 and 21.8% vs. 32.8%, p = 0.002, respectively) and the cumulative live birth rate (17.9% vs. 44.1%, p = 0.027) were significantly higher with the biphasic (5%-2%) O2 concentration strategy. Whole transcriptome analysis of blastocysts donated for research identified 707 RNAs that were differentially expressed in function of the O2 strategy (fold-change > 2, p value < 0.05). These genes are mainly involved in embryo development, DNA repair, embryonic stem cell pluripotency, and implantation potential. The biphasic (5-2%) O2 concentration strategy for preimplantation embryo culture could increase the "take home baby rate", thus improving IVF cost-effectiveness and infertility management.

FISH and Chimps: Insights into Frequency and Distribution of Sperm Aneuploidy in Chimpanzees (Pan troglodytes).

Numerical chromosomal aberrations in sperm are considered to be a major factor in infertility, early pregnancy loss and syndromes with developmental and cognitive disabilities in mammals, including primates. Despite numerous studies in human and farm animals, the incidence and importance of sperm aneuploidies in non-human primate remains mostly undetermined. Here we investigated the incidence and distribution of sperm aneuploidy in chimpanzees (Pan troglodytes), the species closest to human. We identify evolutionary conserved DNA sequences in human and chimpanzee and selected homologous sub-telomeric regions for all chromosomes to build custom probes and perform sperm-FISH analysis on more than 10,000 sperm nuclei per chromosome. Chimpanzee mean autosomal disomy rate was 0.057 ± 0.02%, gonosomes disomy rate was 0.198% and the total disomy rate was 1.497%. The proportion of X or Y gametes was respectively 49.94% and 50.06% for a ratio of 1.002 and diploidy rate was 0.053%. Our data provide for the first time an overview of aneuploidy in non-human primate sperm and shed new insights into the issues of aneuploidy origins and mechanisms.

New insights in Cercopithecinae spermatozoa.

Sperm morphometric and morphologic data have been shown to represent useful tools for monitoring fertility, improving assisted reproduction techniques and conservation of genetic material as well as detecting inbreeding of endangered primates. We provide here for the first time sperm morphologic and morphometric data from Cercopithecus neglectus, Cercopithecus cephus, Papio papio and critically endangered Cercopithecus roloway, as well as comparative data from other Cercopithecinae species, i.e. Allochrocebus lhoesti, Mandrillus sphinx and Papio anubis. Following collection from the epididymis, spermatozoa were measured for each species for the following parameters: head length, head width, head perimeter, head area, midpiece length and total flagellum length, and the head volume, ellipticity, elongation, roughness and regularity were then calculated. Our data are consistent with both the general morphology and the morphometric proportions of Cercopithecinae sperm. Some specificities were observed, with C. cephus displaying a narrow head (width = 2.76 ± 0.26 µM) and C. roloway displaying a short midpiece (6.65 ± 0.61 µM). This data set represents an important contribution, especially for Cercopithecus roloway, one of the most endangered monkeys in the world, and further data on additional specimens coupled to data on mating systems and reproductive ecology should allow a better understanding of the mechanisms underlying these morphological differences across primate species.

ASAP: assemble species by automatic partitioning.

Here, we describe Assemble Species by Automatic Partitioning (ASAP), a new method to build species partitions from single locus sequence alignments (i.e., barcode data sets). ASAP is efficient enough to split data sets as large 104 sequences into putative species in several minutes. Although grounded in evolutionary theory, ASAP is the implementation of a hierarchical clustering algorithm that only uses pairwise genetic distances, avoiding the computational burden of phylogenetic reconstruction. Importantly, ASAP proposes species partitions ranked by a new scoring system that uses no biological prior insight of intraspecific diversity. ASAP is a stand-alone program that can be used either through a graphical web-interface or that can be downloaded and compiled for local usage. We have assessed its power along with three others programs (ABGD, PTP and GMYC) on 10 real COI barcode data sets representing various degrees of challenge (from small and easy cases to large and complicated data sets). We also used Monte-Carlo simulations of a multispecies coalescent framework to assess the strengths and weaknesses of ASAP and the other programs. Through these analyses, we demonstrate that ASAP has the potential to become a major tool for taxonomists as it proposes rapidly in a full graphical exploratory interface relevant species hypothesis as a first step of the integrative taxonomy process.

Customized Frozen Embryo Transfer after Identification of the Receptivity Window with a Transcriptomic Approach Improves the Implantation and Live Birth Rates in Patients with Repeated Implantation Failure.

The aim of this prospective study was to evaluate outcome benefits expected in repeated implantation failure (RIF) patients (n = 217) after customized embryo transfer based upon identification of the receptivity window by transcriptomic approach using the Win-Test. In this test, the expression of 11 endometrial genes known to be predictive of endometrial receptivity is assessed by RT-PCR in biopsies collected during the implantation window (6-9 days after the spontaneous luteinizing hormone surge during natural cycles, 5-9 days after progesterone administration during hormone replacement therapy cycles). Then, patients underwent either customized embryo transfer (cET, n = 157 patients) according to the Win-Test results or embryo transfer according to the classical procedure (control group, n = 60). Pregnancy and live birth rates were compared in the two groups. The Win-Test showed that in 78.5% of women, the receptivity window lasted less than 48 h, although it could be shorter (< 24 h, 9.5%) or longer (> 48 h, 12%). This highlighted that only in 20% of patients with RIF the endometrium would have been receptive if the classical embryo transfer protocol was followed. In the other 80% of patients, the receptivity window was delayed by 1-3 days relative to the classical timing. This suggests that implantation failure could be linked to inadequate timing of embryo transfer. In agreement, both implantation (22.7% vs. 7.2%) and live birth rates per patient (31.8% vs. 8.3%) were significantly higher in the cET group than in the control group. cET on the basis of the Win-Test results could be proposed to improve pregnancy and live birth rates.ClinicalTrials.gov ID: NCT04192396; December 5, 2019, retrospectively registered.