Blastocyst Stage Embryos Research Articles

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.

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? 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. 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. 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. 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). 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. 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. 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. 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. N/A.

Recipients' age, fresh embryo and blastocyst-stage embryo transfer as favorable factors in a transnational oocyte donation program.

In Italy, egg donation is being allowed again following the ruling by the Constitutional Court N. 162/2014. Nevertheless, the number of voluntary donors is insignificant, probably because no reimbursement is provided. Therefore, the great majority of egg donation cycles are performed by using imported cryopreserved oocytes from foreign countries. However, recent evidence has questioned the overall efficacy of this strategy in comparison with the shipment of frozen sperm and vitrified embryos. Retrospective cohort study, conducted at ANDROS Day Surgery Clinic Palermo, Italy in the period 2016-2022, with the objective of evaluating the efficiency of each batch of vitrified oocytes, in terms of completed cycles. The cryopreserved donated oocytes came from a single Spanish clinic (Next Fertility, Valencia, Spain). The primary outcome was the cumulative live birth rate (CLBR). The secondary outcomes were the cumulative ongoing pregnancy rate (COPR), the cumulative clinical pregnancy rate (CCPR) and the miscarriage rate. The CLBR totaled 35.1%, the COPR 36.8%, the CCPR 49.2% and the miscarriage rate 24.7%. In the multivariate analysis, the probability of success was significantly higher in younger recipients, in fresh embryo transfer and in blastocyst-stage embryo transfer. Our "transnational" donation program with vitrified oocytes has good success rates. The main focus of our analysis is the negative effect of advancing recipient age on success rates, outlining a possible, important role of age-related uterine factor on implantation mechanisms. This aspect should be emphasized during the counselling with couples much more than is routinely done.

The effect of sequential embryo transfer on pregnancy outcomes in patients with recurrent implantation failure: a systematic review and meta-analysis of randomized controlled trials.

The aim of our study was to assess the impact of sequential embryo transfer on pregnancy outcomes among patients with recurrent implantation failure (RIF). We conducted a comprehensive search across various databases for eligible clinical trials from inception to January 2024. Randomized controlled trials (RCTs) were included if they compared sequential embryo transfer, comprising both cleavage-stage and blastocyst-stage embryos, with other transfer protocols in infertile women with repeated implantation failure. Meta-analysis was performed using Revman software. Our primary focus was on the ongoing pregnancy rate. Our secondary measures included rates of chemical pregnancies, clinical pregnancies, miscarriages, and multiple pregnancies. Seven RCTs, encompassing 909 patients, met the inclusion criteria. Sequential embryo transfer demonstrated a significant increase in the ongoing pregnancy rate compared to the control group (OR = 2.28, 95% CI [1.46, 3.56], p = 0.003). Moreover, the sequential embryo transfer group exhibited notable improvements in chemical and clinical pregnancy rates. There were no statistically significant differences between the groups regarding multiple pregnancy and miscarriage rates (p > 0.05). Sequential embryo transfer shows promise in enhancing pregnancy outcomes among RIF patients. However, additional trials are warranted to validate our findings.

Putrescine supplementation improves the developmental competence of in vitro produced bovine embryos

The aim of this study was to investigate the effect of putrescine, anti-apoptotic, antioxidant, and a cell proliferation stimulant, on embryo development and quality by supplementing it to in vitro culture medium. In this study, oocytes were obtained from the ovaries of Holstein cattle. Following maturation and fertilization, the presumptive zygotes were randomly assigned to two groups. The first group (Putrescine, n = 435) was supplemented with putrescine at a concentration of 0.5 mM to in vitro culture. The second group (n = 407) was maintained under standard culture conditions without any supplementations to the medium. Following the determination of the developmental stages of the embryos, only those in the blastocyst stage were subjected to differential staining and the cell numbers of the embryos were determined. Moreover, the TUNEL assay was employed to ascertain the extent of cell death and the apoptotic index in the embryos. Additionally, the levels of ROS were determined in the embryos. Furthermore, gene expression analyses were conducted on blastocyst-stage embryos to ascertain the potential of putrescine supplementation in embryo development along specific pathways. Following in vitro culture, the blastocyst formation rate was 44.37 % in the putrescine group and 32.97 % in the control group (P < 0.05). The counts of ICM (60.60 ± 15.79 vs 50.73 ± 16.74), TE (117.70 ± 23.67 vs 94.0 ± 22.46), and TCC (178.30 ± 26.15 vs 144.73 ± 26.86) were found to be statistically higher in blastocysts developing after putrescine supplementation compared to the control group. Furthermore, the number of apoptotic cells (7.69 ± 2.17 vs 9.96 ± 3.99) and the apoptotic index (5.07 % vs 8.01 %) were found to be lower in the putrescine group in comparison to the control group. Nevertheless, it was established that the ROS level in the control group was approximately two-fold higher than in the putrescine group (P < 0.05). The findings also revealed that putrescine up-regulated the gene expression of SOD, GPX4, CAT, BCL2, NANOG and GATA3 while simultaneously down-regulating the BAX expression level. In conclusion, the supplementation of putrescine to the culture medium during in vitro bovine embryo production was found to contribute to the improvement of embryo quality and early embryonic development.

Modern aspects of preimplantation genetic testing of embryos in assisted reproductive technology programs (literature review)

Background. The success of assisted reproductive technologies depends on many factors, the main ones being the quality and genetic status of the embryo and endometrial receptivity. Preimplantation genetic testing is a tool that aims to reduce the risk of selecting an aneuploid embryo for transfer. Disputes surrounding the use of preimplantation genetic testing are conducted in the context of older patients, with recurrent miscarriage, with genetic karyotype abnormalities in a married couple, as well as multiple unsuccessful attempts at ART in the anamnesis.Purpose of review. To summarize and analyze the available data on current trends in the use of preimplantation genetic testing (PGT-A).Materials and methods. The review includes published data over the past 10 years regarding the effectiveness of ART programs and pregnancy outcomes after the use of preimplantation genetic testing. The literature search was conducted in Medline, Scopus, Web of Science, Google Scholar, PubMed, Wiley and Cochrane Library databases.Results. According to most authors, preimplantation genetic testing does not improve live birth rates per patient in the general population, but it does improve live birth rates when performing PGT-A on blastocyst-stage embryos in women over 35 years of age, as well as in women with a history of pregnancy loss to reduce risk miscarriage of a subsequent pregnancy.Conclusion. Preimplantation genetic testing is a valid method for assessing euploidy and mosaicism of an embryo before transfer. The feasibility of use, according to research results, is more related to conditions in which the risk of embryonic aneuploidy may increase, and is justified in high-risk patients, while the use of this technique in patients with a good prognosis is still questionable. First, trophectoderm biopsies may not reflect the ploidy of the inner cell mass. Secondly, even if we assume that this is the case, we cannot be sure that the embryonic cell line will not self-correct. In other words, once a diagnosis of PGT-A is received suggesting mosaicism or aneuploidy, the likelihood of a false-positive diagnosis is high.

Cumulative live birth rate of a blastocyst versus cleavage stage embryo transfer policy during in vitro fertilisation in women with a good prognosis: multicentre randomised controlled trial

ObjectivesTo evaluate whether embryo transfers at blastocyst stage improve the cumulative live birth rate after oocyte retrieval, including both fresh and frozen-thawed transfers, and whether the risk of obstetric and...

Optimization of donor cell production for somatic cell nuclear transfer in the critically endangered Vietnamese Ỉ pig

We aimed to establish efficient donor cells to produce piglets by somatic cell nuclear transfer (SCNT) of the endangered Vietnamese Ỉ pig. In Experiment 1, we assessed the effects of cell passages on the in vitro development of SCNT embryos. Cells with five and six passages showed significantly cleaved and blastocyst formation rates (86.72 and 86.64; 35.68 and 35.51, respectively, P < 0.05). The highest average total cell number per blastocyst was observed in groups of cells with five and six passages (50.45 and 50.18, respectively). Experiment 2 was performed to assess the sex of donor cells on the subsequent development of SCNT embryos. There was no significant difference in the cleaved and blastocyst formation rates, and the average total cell between female and male groups (86.51 % vs 86.94 % and 35.31 % vs 35.08 %, 50.29 % vs 50.67 %, respectively, P > 0.05). Experiment 3 was performed to assess the effect of cell lines on the development of SCNT embryos. Our results showed no significant difference in the success rate of fibroblast nuclear transfer into recipient oocytes, the cleaved and blastocyst formation rates, and the average total cell number per blastocyst among the cell lines 6004, 9154, 9155, 9156 and 9157 (P > 0.05). Experiment 4 was performed to assess the ability of SCNT embryos to induce pregnancy and to develop term. SCNT embryos were produced from Ỉ fibroblast cells established based on the results of Experiments 1, 2 and 3. Transfer of blastocyst stage embryos into 19 recipients (100–120 embryos in each) resulted in 14 pregnancies, in which 8 pregnant females terminated on Day 22–42 and 6 others produced 20 cloned piglets from donor cells of a female pig but 5 piglets died before birth and 15 healthy cloned piglets. However, 3 out of 15 healthy piglets died of unknown causes within 24h of birth and 3 out of 15 healthy piglets died at 3–5 days of age due to diarrhoea, 9 out of 15 healthy piglets are now 3 months of age. Finally, we established a protocol for the donor cell production which enabled the production of the endangered Ỉ pig embryos by SCNT and maximized blastocyst production rate by more than 35 % and pregnant rate after the transfer of cloned Ỉ pig embryos to recipients at 73.68 % for the first time in Vietnam.

Effect of single blastocyst-stage versus single cleavage-stage embryo transfer on cumulative live births in women with good prognosis undergoing in vitro fertilization: Multicenter Randomized Controlled Trial

In this multicenter, non-inferiority, randomized trial, we randomly assigned 992 women undergoing in-vitro fertilization (IVF) with a good prognosis (aged 20-40, ≥3 transferrable cleavage-stage embryos) to strategies of blastocyst-stage (n = 497) or cleavage-stage (n = 495) single embryo transfer. Primary outcome was cumulative live-birth rate after up to three transfers. Secondary outcomes were cumulative live-births after all embryo transfers within 1 year of randomization, pregnancy outcomes, obstetric-perinatal complications, and livebirths outcomes. Live-birth rates were 74.8% in blastocyst-stage group versus 66.3% in cleavage-stage group (relative risk 1.13, 95%CI:1.04-1.22; Pnon-inferiority < 0.001, Psuperiority = 0.003) (1-year cumulative live birth rates of 75.7% versus 68.9%). Blastocyst transfer increased the risk of spontaneous preterm birth (4.6% vs 2.0%; P = 0.02) and neonatal hospitalization >3 days. Among good prognosis women, a strategy of single blastocyst transfer increases cumulative live-birth rates over single cleavage-stage transfer. Blastocyst transfer resulted in higher preterm birth rates. This information should be used to counsel patients on their choice between cleavage-stage and blastocyst-stage transfer (NCT03152643, https://clinicaltrials.gov/study/NCT03152643).

Live Birth after Cleavage-Stage versus Blastocyst-Stage Embryo Transfer in Assisted Reproductive Technology: A Randomised Controlled Study.

Blastocyst stage transfer appears to improve pregnancy outcomes. The aim of this study is to evaluate the pregnancy results between fresh cycle blastocyst stage embryo transfer and cleavage stage embryo transfer in patients who undergo intracytoplasmic sperm injection (ICSI). This randomised clinical trial study was conducted at the Infertility Research Centre of Milad Hospital in Mashhad, Iran from 2018 to 2020 on 240 infertile women who presented for their first ICSI procedure. These patients were assigned to receive either cleavage embryo transfer (n=112) or blastocyst stage transfer (n=107). Pregnancy outcomes were measured in both groups. There were no differences regarding age, body mass index (BMI), serum follicle-stimulating hormone (FSH), duration of infertility, and aetiology of infertility between the groups (P>0.05). There were more follicles, total oocytes, and metaphase II (M2) oocytes in the blastocyst stage group. Considerably more cleavage stage embryos were transferred compared to the number of transferred blastocysts (P=0.001). The blastocyst group had more vitrified embryos than the cleavage group (P=0.000). The rates of implantation (P=0.332), chemical pregnancy (P=0.165), clinical pregnancy (P=0.694), and live births (P=0.727) were higher in the blastocyst group, but they were not significantly different. The rate of abortion was also not significantly higher in the blastocyst group (P=0.296). Blastocysts transferred in the fresh cycle of an ICSI procedure may be more advantageous compared to cleavage stage embryo transfer (registration number: IRCT20181030041503N1).

P-745 effectiveness and safety of consecutive single embryo transfer compared to double embryo transfer: results from UK HFEA registry

Abstract Study question How does two-consecutive single embryo transfer (2xSET) affect reproductive outcomes of in-vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) compared to double embryo transfer (DET)? Summary answer 2xSET may provide greater or comparable live birth rates with lower multiple birth, preterm birth, and pregnancy loss or neonatal death rates compared to DET. What is known already Elective single embryo transfer (SET) in IVF/ICSI is widely encouraged over DET to minimise the risk of multiple birth and associated morbidities. Despite this, UK multiple birth rates following IVF remain higher than spontaneous conception, with 5% of IVF pregnancies resulting in multiple birth compared to 0.4%-1.2% multiple gestation rates following spontaneous conception. Owing to advancements in cryopreservation techniques, live birth and ongoing pregnancy rates are now comparable between fresh and frozen embryo transfer. Consequently, 2xSET has been suggested as an alternate technique to achieve comparable live birth rates with fewer multiple gestation pregnancies compared to DET. 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. Within this analysis, all women who underwent their first oocyte collection and IVF or ICSI treatment cycle with subsequent SET, DET or 2xSET between 2010 and 2019 using either blastocyst or cleavage stage embryos were included (N = 125,149). Participants/materials, setting, methods This national retrospective cohort study utilised UK HFEA register data from 2010-2019, including all women who underwent their first oocyte collection and subsequent embryo transfer (N = 125,149). The rate of live birth, multiple birth, preterm birth, and pregnancy loss or neonatal death was compared between SET, DET, and 2xSET IVF/ICSI pregnancies using either blastocyst or cleavage stage embryos, and was stratified by maternal age. Data analysis was conducted in RStudio v4.2, alpha equals 0.05. Main results and the role of chance 2xSET pregnancies following blastocyst-stage transfer achieved a greater live birth occurrence rate of 0.47 (0.13) (median (interquartile range)) than SET, 0.41 (0.13), and DET, 0.38 (0.13) (P &amp;lt; 0.05). When using SET as a reference standard, 2xSET achieved a lower multiple birth rate, odds ratio (OR) of 6.87 (95%CI 6.14-7.68), than DET, OR 28.20 (95%CI 25.20-31.57), and lower preterm birth rate; OR 1.11 (95%CI 1.06-1.15) in 2xSET, and OR 2.80 (95%CI 2.67-2.94) in DET. Pregnancy loss or neonatal death rate was also lower in 2xSET, OR 1.14 (95%CI 1.08-1.21), compared to DET, OR 2.11 (95%CI 1.98-2.24). Conversely, in cleavage-stage embryo transfer pregnancies, no significant difference in live birth occurrence rate was observed, achieving rates of 0.27 (0.21) for SET, 0.26 (0.13) for DET, and 0.29 (0.18) for 2xSET. 2xSET was less likely to result in multiple birth than DET, OR 0.14 (95%CI 0.11-0.19). Moreover, when using SET as a reference standard, 2xSET was less likely to result in preterm birth than DET, OR 1.02 (95%CI 0.87-1.23) and 2.48 (95%CI 2.17-2.82) respectively, as well as pregnancy loss or neonatal death, OR 1.07 (95%CI 0.85-1.35) and 2.03 (95%CI 1.70-2.42) respectively. Limitations, reasons for caution Certain confounders are not recorded within HFEA registry data, including patient body mass index (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 2xSET may provide greater or comparable live birth rates with lower multiple birth and morbidity than DET. Promotion of 2xSET where appropriate for maternal age and embryo quality should be implemented to enhance reproductive outcomes and reduce the risk of morbidity in IVF/ICSI pregnancies. Trial registration number Not Applicable

P-170 Clinical evaluation of an image-based artificial intelligence model for embryo selection: a double-blinded randomized comparative reader study

Abstract Study question What is the performance of an image-based artificial intelligence (AI) model for ranking blastocyst stage embryos compared to embryologists using traditional morphology? Summary answer The AI was non-inferior to manual embryo selection. The AI showed significant improvement in clinical pregnancy when there was disagreement between AI and manual selection. What is known already In previous work, we developed an image-based AI model that predicts the likelihood of clinical pregnancy by analyzing a single static image of a blastocyst captured prior to biopsy or freeze. This model was trained on data from over 8,000 single-blastocyst transfer cycles from multiple U.S. IVF clinics performed between 2014 to 2021. Study design, size, duration We performed a retrospective, double-blinded, comparative reader study. The study included data from 438 single-blastocyst transfers from 10 different IVF clinics in U.S. that were not part of previous model development or testing. Using this data, a set of 1,257 virtual patient panels were created. Each virtual patient panel included between 2-5 embryos that were matched by age (18 - 29, 30 - 34, 35 - 37, ≥38), race (white, non-white, and unknown) and PGT-status. Participants/materials, setting, methods A group of 5 embryologists (readers) with varying levels of experience were asked to select their top embryo for transfer for each virtual patient panel (control arm) based on morphology grades. The AI model was also used to select a top embryo for transfer from each patient panel (treatment arm). The clinical pregnancy rates of the top-selected embryos were calculated and compared. Main results and the role of chance There was disagreement on the top pick embryo amongst the five embryologists 34.6% of the time, which increased to 43.9% when there were 3 or more embryos to choose from, supporting the need for a tool to standardize this decision. The clinical pregnancy rate of the control arm (average of embryologist readers) was 61.0% (individual rates of 58.9%, 59.6%, 61.5%, 61.6%, and 63.3%), and the clinical pregnancy rate of the treatment arm (AI model) was 62.3% (demonstrating non-inferiority with p&amp;lt;.001). The pregnancy rate of random embryo selection was 53.2%. All 5 of the embryologist readers agreed on the top-pick embryo 65% of the time. When all 5 readers agreed, the AI model disagreed with that consensus 31% of the time, and in these cases the AI model pregnancy rate was significantly higher by 8.6% (AI: 63.1%, Embryologist Consensus: 54.5% (p &amp;lt; 0.05)). Limitations, reasons for caution While data for this study was collected prospectively, the analysis was done retrospectively. Furthermore, readers were provided morphology grades from retrospective data rather than grading the embryos themselves. However, it is common for an embryologist to make an embryo selection based on morphology grades previously assigned by a different embryologist. Wider implications of the findings The AI model was able to select the top embryo for transfer with performance comparable to experienced embryologists. Such a model could allow for automated and objective embryo selection using a single static image of blastocyst stage embryos. Trial registration number NA

P-548 An investigation into the mechanisms of active enhancers regulating the initial lineage differentiation in mammals

Abstract Study question What role do active enhancers play in determining the fate of early embryonic cells? Are there differences in active enhancers between mouse and human blastocysts? Summary answer Tissue-specific active enhancers in inner cell mass (ICM) and trophoblast (TE) are essential for blastocyst formation, regulating gene expression through interactive loops with promoters. What is known already At the two-cell stage of nuclear transfer embryos, the absence of interaction between Zscan4d promoter and distal active enhancer leads to reduced Zscan4d expression, resulting in lower developmental rates. Overexpressing the demethylase Kdm4d alleviates reprogramming-resistant H3K9me3 modification, restoring the structural loop between the Zscan4d promoter and active enhancer and enhancing developmental efficiency. These findings strongly suggest a close association between the formation of regulatory chromatin interactions in early embryonic development and histone modifications. Indicating active enhancers marked with H3K27ac may regulate differentiation gene expression through distal interactions in blastocyst. Study design, size, duration Analyze variations in histone H3K27ac modification, chromatin accessibility, higher-order structures, and transcriptomes during mouse embryo differentiation from 8-cell stage to ICM and TE formation. Identify tissue-specific active enhancers in ICM and TE, validate their gene expression regulation, explore their role in early differentiation-associated genes in mice. Compare and clarify similarities and differences in enhancer regulation mechanisms during early embryo development in humans and mice. Participants/materials, setting, methods The 8-cell, morula and blastocyst stage embryos were collected from the oviducts and uterus of super-ovulated female ICR mice mated with male mice. The clinical human blastocysts were collected and separated the ICM and TE. Low-input multi-omics sequencing, including Cut-Tag, ATAC-seq, Hi-C, and RNA-seq, was performed on the embryonic samples. After analyzing and identifying active enhancers, tissue-specific ones were selected and validated for their impact on gene expression via CRISPR-Cas9 knockout in embryos. Main results and the role of chance Inhibiting ep300 expression in mouse embryos through siRNA interference reduces blastocyst formation from 90% to approximately 40%. Introducing the small molecule inhibitor A485 at the 8-cell stage, blocking the active center of CBP/p300 enzymes, completely arrests embryos at the morula stage, preventing their development into blastocysts. Emphasizing the crucial role of correctly establishing active enhancers marked by H3K27ac modification in embryonic differentiation. Multi-omics data demonstrates high repeatability and quality. PCA clustering analysis reveals a clear differentiation path in the distribution of H3K27ac-modified histones, chromatin accessibility sites, and the transcriptome from the 8-cell stage to the blastocyst. Differences in H3K27ac histone modification distribution between the ICM and TE indicate the presence of tissue-specific active enhancers in blastocyst. The disparities in H3K27ac modification distribution between blastocyst ICM and TE primarily occur in distal gene regions rather than proximal ones. Moreover, these distal enhancers exhibit a positive correlation with the expression of lineage-specific genes, suggesting a probable regulatory role of distal enhancers in gene modulation during embryonic differentiation. Tissue-specific enhancer-promoter (EP) interaction loops emerge during embryonic differentiation, allowing direct interaction between tissue-specific active enhancers and promoters, thereby activating the expression of tissue-specific genes. Limitations, reasons for caution While DNA sequences with H3K27ac modification are currently considered markers for active enhancers, H3K4me modification is another histone marker for enhancers. However, enhancers associated with H3K4me modification may not necessarily be in an activated state. Future research can simultaneously incorporate appropriate detection methods for H3K4me modification. Wider implications of the findings After elucidating the mechanisms through which active enhancers regulate mouse differentiation, comparing the differences in active enhancers during the first lineage differentiation process between mice and humans can help identify factors that enhance human blastocyst quality. This can potentially improve clinical outcomes in assisted reproduction. Trial registration number not applicable

P-110 Live birth of blastocyst culture in women with previous poor blastocyst formation: a cohort study

Abstract Study question Do cumulative live birth rates(CLBRs) in the second cycle differ between blastocyst-stage and cleavage-stage transfer in women with low blastocyst progression during initial IVF ? Summary answer The CLBRs following subsequent oocyte retrievals were comparable for extended culture with blastocyst-stage embryo versus cleavage-stage transfers. What is known already Fresh blastocyst-stage embryo transfer increases live birth rates when compared to cleavage- stage embryo transfer in women with good prognosis. However, it remains unclear whether a blastocyst-culture approach can still be considered for women with a history of failed or reduced blastocyst formation. Study design, size, duration A retrospective cohort study evaluating outcomes of the second IVF/ICSI in women who had a history of poor blastocyst development in their first-time retrievals at a single fertility center from September 2019 to December 2021. Women fulfilled embryo quality criteria of having at least two good-quality cleavage-stage embryos (graded 1-2) on day 3 were included for analysis. Participants/materials, setting, methods A total of 396 patients were analyzed and categorized into two groups. Group D5/6: Extending culture of all embryos to blastocyst-stage in vitro followed by blastocyst transfer; Group D3: transfer or cryopreservation of one or two of the highest quality cleavage-stage embryo(s) on Day3.The main outcome measure was the CLBR per oocyte retrieval.Multivariable logistic regression analyses were used to assess the association between two culture approaches and live birth outcomes after adjusting for possible confounders. Main results and the role of chance The CLBRs (57.01% versus 49.48%) were numerically higher in women in D5/6 group (N = 107) than those in D3 group (N = 289) although the difference was attenuated and did not reach statistical significance after controlling for confounders (aOR: 1.27, 95%CI 0.78, 2.07,P=0.345). All subgroup analyses showed similar conclusions as the main model, even restricting on women with a limited number of quality embryos 3 days post-fertilization. Among cycles with only 2 or 3 good-quality cleavage embryos, Day3 transfers were still associated with lower CLBR compared to all blastocyst culture and transfer (aOR 0.66, 95% CI 0.51-0.87). Limitations, reasons for caution The retrospective nature of the present study, alongside the selection bias towards blastocyst culture, may predispose to the risk of residual confounding. The cohort of women characterized by previous failed or reduced blastocyst formation was comparatively small. Larger prospective studies focusing on the unique group are still needed. Wider implications of the findings Even in poor prognosis IVF patients with a history of poor blastocyst formation and/ or blastulation failure, all blastocyst culture and transfer can still be considered when at least two good-quality embryos are available at day 3. These findings are clinically relevant and require additional investigation. Trial registration number Not Applicable

P-770 Health outcomes of taiwanese infants after different embryo stages in both fresh and frozen transfer procedures

Abstract Study question Does freezing embryos have any effects on neonatal and postnatal health? Does extended embryo culture have any impact on these health outcomes? Summary answer frozen embryo transfer (FET) infants were more likely be large gestational age, but with lower odds of recurrent upper respiratory infection and dermatitis. What is known already Infants born from frozen embryo transfers tend to have higher birth weights and are less likely to be small for gestational age. There are no notable variations in congenital malformations or child development. However, there’s a lack of long-term follow-up data. Study design, size, duration In this retrospective cohort study conducted in Taiwan, data from the national assisted reproductive technology (ART) database spanning from January 1st, 2013, to December 31st, 2017, was utilized. The study categorizes cases into fresh and frozen embryo transfer groups, with additional subdivisions based on cleavage and blastocyst stage transfers. Singletons born in each group were then linked to the National Health Insurance Database for follow-up on health conditions until December 13th, 2018. Participants/materials, setting, methods We collected data on singleton births resulting from assisted reproductive technology procedures performed in Taiwan from January 1st, 2013, to December 31st, 2017. Our analysis included 10,669 eligible infants. We investigated factors such as gestational age, birth weight, and various systemic diseases, encompassing neurological disorders, facial and eye abnormalities, cardiovascular diseases, respiratory disease, gastrointestinal disorders, renal system disorders, musculoskeletal disorders, skin and submucous disorders, chromosomal abnormalities, infections, and birth injuries. Main results and the role of chance Compared to infants conceived from fresh embryos, those born to mothers who underwent frozen embryo transfer (FET) were more likely to be large for gestational age (OR 1.63, 95% CI 1.30-2.04 for blastocyst and OR 1.69, 95% CI 1.36-2.10 for cleavage stage), and to have a neonatal birth weight of ≥ 4000g (OR 1.88, 95% CI 1.15-3.07 for blastocyst and OR 2.64, 95% CI 1.63-4.28 for cleavage stage). However, they were less likely to be small for gestational age (OR 0.68, 95% CI 0.56-0.82 for blastocyst and OR 0.68, 95% CI 0.56-0.82 for cleavage stage). Infants born from frozen embryo transfers also experienced lower odds of recurrent upper respiratory infection (OR 0.72, 95% CI 0.60-0.86 for blastocyst and OR 0.60, 95% CI 0.52-0.69 for cleavage stage), as well as eczema and dermatitis (OR 0.75, 95% CI 0.62-0.91 for blastocyst and OR 0.75, 95% CI 0.62-0.91 for cleavage stage). There was no observed effect on infant health between blastocyst and cleavage stage embryo transfers. Limitations, reasons for caution Our retrospective study design may not possess the same level of rigor as a randomized controlled trial (RCT). The follow-up period in our study ranged from 1 to 5 years, and some diseases may not manifest within this short-term timeframe, necessitating longer-term tracking for more comprehensive observation. Wider implications of the findings The result highlights the potential benefits of FET in reducing the risk of low birth weight. The observed decrease respiratory infections and skin disorders among FET infants suggests a possible advantage in immune system development or environmental adaptability. Further research with longer-term tracking is warranted. Trial registration number KMUHIRB-E(I)-20210222

O-148 Does presence of endometriosis adversely affect oocyte morphology? Evaluation of a large number of oocytes obtained from endometriosis patients, 27204 oocytes

Abstract Study question Does presence of endometriosis adversely affect oocyte morphology? Evaluation of a large number of oocytes obtained from endometriosis patients, 27204 oocytes Summary answer In the presence of endometriosis, oocyte morphology is not impaired. The rate of reaching blastocyst and fertiilization rate, also pregnancy outcomes are not affected negatively. What is known already Although there are hypothesis, theories that altered steroidogenesis and folliculogenesis, higher oxidative stress, reactive oxygen species, altered cell cycle progression, inflammation and angiogenesis in the follicular environment exposes oocytes to a hostile inflammatory environment and alters oocyte quality. There has been much debate and conflicting evidence as to whether the poorer IVF outcomes in women with endometriosis is related to altered oocyte quality. There is some evidence to suggest that impaired oocyte morphology in women with endometriosis may have an adverse impact on fertilization rate, however, most studies have shown that there is no difference in pregnancy outcomes following IVF. Study design, size, duration This retrospective, single center study evaluated 29130 ART cycles from August 2011 to March 2023,based on data obtained from Istanbul Memorial Hospital,ART and Reproductive Genetics Center.Study group included endometriosis patients(n = 4602 cycles, 27204 oocytes) and control group included non-endometriosis patients(n = 24528 cycles, 178774 oocytes).We analyzed demographic and cycle characteristics, oocyte morphology in ART cycles between the two groups.Futhermore, we compared pregnancy outcomes in frozen-thawed embryo transfer(FET) cycles (total number:11116 FET cycles; endometriosis group:2255 cycles,non-endometriosis group:8861 cycles). Participants/materials, setting, methods Patients diagnosed with endometrioma by ultrasound, diagnosed with endometriosis by laparoscopy or patients who underwent endometrioma surgery or adenomyosis detected on ultrasound were included in the study (endometriosis) group. In the control group, the patients without endometriosis were included. Mann Whitney U test and Pearson Chi-square test used. Cliff's Delta effect size (????) for non-parametric tests and Phi effect size (p) for categorical data were reported. Main results and the role of chance The sample was very large, so the statistical results were given in terms of effect size, not only p value calculated. Female age was similar. Female body mass index, number of previous cycles, duration of infertility, AMH, total gonadotropin dosage used, duration of ovarian stimulation, estradiol level on trigger day, number of aspirated oocytes, mature and fertilized oocytes, maturation and fertilization rate, rate of blastulation, rate of usable blastocyst (top and good quality), number of embryos transferred, blastocyst stage embryo transfer cycles were statistically different between the two groups (p &amp;lt; 0.001). However when the effect size examined, all variables were found to have a negligible association by Cliff's Delta or Phi effect size calculations. Oocytes obtained from endometriosis patients had statistically significantly higher severe central granulation, large perivitellin space, thick zona, polar body defect abnormalities compared to non-endometriosis patients (p &amp;lt; 0.001), Phi effect size showed negligible association for all variables. In endometriosis group compared to non endometriosis group; biochemical pregnancy (68.9% vs 72.2%, p:0.002, Phi:0.030), clinical pregnancy (61.5% vs 64.5%, p:0.007, Phi:0.025), total pregnancy loss (22% vs 24.4%, p:0.05, Phi:0.022) were statistically higher, but Phi effect sizes were negligible. Live birth were similar (52.5% vs 53.2 P:0.56) between the two groups. Limitations, reasons for caution The principal limitation of the study is retrospective design of the analysis. But the strength of the study is that included 27204 oocytes from endometriosis patients. Wider implications of the findings To our knowledge, this study includes the largest case group that investigates the endometriosis and oocyte morphology. The results show that endometriosis does not have a negative impact on oocyte morphology. Additionally, it has been shown that the presence of endometriosis does not have a negative effect on pregnancy outcomes. Trial registration number *

P-252 Non-invasive artificial intelligence (AI) prediction of blastocyst development from mature oocytes unveils correlation with blastocyst ploidy for enhanced reproductive insight at earliest stage of development

Abstract Study question Can MAGENTA identify mature oocytes more likely to develop into a blastocyst of euploid status? Summary answer Although built to predict blastocyst development, MAGENTA analysis of mature oocytes additionally displays the ability to highlight those with higher potential to become euploid embryos. What is known already MAGENTA (AI image-analysis tool) has been trained to assess and predict blastocyst stage embryo development from mature, denuded oocytes. MAGENTA scores consistently identify oocytes of better quality – more likely to develop into a blastocyst, including blastocysts of higher morphological quality. However, in addition to achieving a blastocyst, the ploidy status of that embryo is crucial in dictating overall chances of implantation and cycle success. Although MAGENTA was not trained to predict blastocyst ploidy from oocytes, most chromosomal errors are of maternal meiotic origin. A correlation between MAGENTA and ploidy status would ignite research possibilities and provide valuable insights. Study design, size, duration A retrospective dataset of 1,324 blastocyst embryos that underwent PGT-A via NGS sequencing, between the years 2021-2023, was assessed. All embryos that were tested for ploidy from a patient cohort were included. Embryos reported as mosaic or ‘no diagnosis’ were excluded from analysis (N = 169). All embryos were cultured in a time-lapse incubator immediately post-ICSI. Of the biopsied blastocysts, 81% were of good morphological quality (expansion grade 1-6, ICM and TE grade A/B). Participants/materials, setting, methods The data includes 292 patients with a mean age of 38.5 (range 19-46) and an average number of tested blastocysts of 4 (range 1-14). Of the 1173 blastocysts, 847 were aneuploid (72.2%) and 326 were euploid (27.8%). 83% of the blastocysts were from patients of advanced maternal age (AMA, ≥38years old). The first time-lapse image, capturing the mature oocyte stage, was extracted, and scored by MAGENTA (scale 0-10). MAGENTA scores were compared by Welch’s t-tests. Main results and the role of chance Impressively, oocytes that developed into euploid blastocysts (n = 326) were identified by MAGENTA with a higher average score of 6.8 compared to those that developed into aneuploid blastocysts (n = 847) with a score of 6.4; a statistically significant differentiation (p &amp;lt; 0.05). 80% of the dataset were high quality blastocysts (expansion 4-6, ICM and TE grade A/B) with an imbalance of euploid (n = 295; mean score 6.8) and aneuploid (n = 643; mean score 6.6) blastocysts—likely a result of AMA. Therefore, subgroup analysis was focused on assessing the ploidy status relationships amongst several patient age groups within these AMA cases. Due to our clinic’s indication for PGT-A, the smallest subset of oocytes was from patients &amp;lt;38 years of age (N = 373, 48% euploid). In this age group there was no significant difference in MAGENTA scores between the oocytes of euploid and aneuploid embryo status (6.9 vs 6.7; p = 0.522). However, in oocytes from patients aged ≥38 (N = 800, 19% euploid), the distinction between those that became euploid and aneuploid blastocysts is evident with a statistically significant difference in MAGENTA scores (6.8 vs 6.3; p &amp;lt; 0.05). This relationship with ploidy status additionally remains with further stratification into the ≥41 age group (N = 467 oocytes, 13% euploid; 6.7 vs 5.9; p &amp;lt; 0.01). Limitations, reasons for caution Majority of the patients in this dataset underwent PGT-A due to AMA, further research is required to include a wider age demographic, particularly in patients &amp;lt;35 years old. Greater representation of varying blastocyst qualities is required to further assess MAGENTA correlation to ploidy outcomes amongst quality groups. Wider implications of the findings This study presents the first non-invasive assessment of mature oocyte quality that indicates oocytes with greater potential for euploid blastocyst development. This application of MAGENTA provides a novel method of gaining ploidy status potential at the mature oocyte stage, which is invaluable to both IVF and cryopreservation cycles. Trial registration number NOT APPLICABLE

O-251 Generative artificial intelligence substantially enhances the accuracy of embryo selection models

Abstract Study question Can generative artificial intelligence (AI) produce high-fidelity human embryo images to improve AI-based embryo selection models? Summary answer Generative AI models exhibit the capability to generate high-fidelity human embryo images and can substantially improve the performance of AI models through extensive training data. What is known already The integration of AI into in vitro fertilization (IVF) procedures holds the potential to enhance objectivity and automate embryo selection for transfer. However, the effectiveness of AI is limited by data scarcity and ethical concerns related to patient data privacy. Generative Adversarial Networks (GAN) have emerged as a promising approach to alleviate data limitations by generating synthetic data that closely approximate real images. However, the advantage of applying GAN in IVF embryo images is yet to be determined. Study design, size, duration Embryo images were retrieved as training data from time-lapse microscopy (TLM) videos (n = 328). Embryo key morphokinetic variables including blastomere division from 1-cell stage to 9 (and more) cells-stage, compaction of morula, and blastocyst formation were manually annotated by six embryologists. A style-based GAN was fine-tuned as the generative model and a residual network as the morphokinetic classification model. Participants/materials, setting, methods We configured generative models with data augmentation (AUG) and pretrained weights (Pretrained-T/R) to test their refinement to synthetic image quality. We analyzed quantitative metrics including Fréchet Inception Distance (FID) and Kernel Inception Distance (KID) to assess the quality and fidelity of the generated images. Subsequently, we evaluated qualitative performance through a visual Turing test. Then, we compared the performance of a classifier by training real images alone and by integrating real images with generated data. Main results and the role of chance During the training process, we observed consistent improvement in image quality that was measured by FID and KID scores. The AUG+Pretrained-R model showed the highest performance of the evaluated five configurations with FID and KID scores of 15.2 and 0.004 following 5,000 training iterations. Subsequently, we carried out a visual Turing test, such that a total of 60 individuals including IVF embryologists (Group I, n = 25), IVF laboratory technicians (Group II, n = 15), and non-experts (Group III, n = 20) evaluated the synthetic blastocyst-stage embryo images. Group I displayed accuracy of 55.7% (±6.2), sensitivity of 65.9% (±14.1), and specificity of 45.1% (±17.8). Group II showed accuracy of 54.2% (±4.7), sensitivity of 65.9% (±17.6), and specificity of 42.0% (±19.6). Group III had the accuracy of 50.1% (±3.8), sensitivity of 49.3% (±6.3), and specificity was 50.9% (±10.4). Statistical analysis indicated significant differences in accuracy (Kruskal-Wallis test, P=1.2x10-3) and sensitivity (Kruskal-Wallis test, P=1.6x10-4) among the three groups. In the embryonic stage classification model, integrated with generated data outperformed the model using real data solely, with an increase of validation accuracy from 72.6% to 90.6%. The classifier was tested on external TLM video data (n = 100) where the area under the curve was 0.92. Limitations, reasons for caution Further research is needed to involve a more extensive and diverse dataset, e.g. video generation, and more detailed annotations including polar body appearance, pronuclei appearance and disappearance, and blastocyst expansion and hatching. Wider implications of the findings Generative AI offers potential in generating high-fidelity human embryo images. This approach ensures sufficient training datasets while addressing class imbalances for robust AI-based methods, ultimately transforming embryo selection and enhancing IVF outcomes. A set of 5,000 generated images (1024x1024-pixel) at each embryonic developmental stage was open-source for future AI studies. Trial registration number not applicable

P-277 Focal rather than diffuse nature of adenomyosis might be more detrimental to IVF outcomes after single euploid embryo transfer

Abstract Study question Is the nature of adenomyosis a factor to consider after a single euploid embryo transfer? Summary answer Focal adenomyosis was associated with lower live birth rate per transfer when compared to diffuse adenomyosis. What is known already Adenomyosis is widely described to hamper reproductive potential of women who suffer it. This uterine pathology has a detrimental impact on in vitro fertilization (IVF) clinical outcomes, as described by a series of recent metanalysis. Nevertheless, there is scarce evidence regarding clinical studies that address the impact of adenomyosis depending either on its diffuse or focal nature. Study design, size, duration A multicenter retrospective cohort study in which 229 patients undergoing IVF treatment were included. Patients with single embryo transfer (SET) in blastocyst stage after pregestational testing for aneuploidy (PGT-A) between years 2015 and May 2023 were divided into two groups: diffuse adenomyosis (n = 167) and focal adenomyosis (n = 62). Participants/materials, setting, methods Inclusion criteria consisted of patients in a PGT-A program who had a cryotransfer of a single euploid blastocyst-stage embryo. Patients were diagnosed within our facilities using transvaginal ultrasonography (TVUS) prior to their IVF cycle. Diffuse adenomyosis was diagnosed when irregular endometrial-myometrial junction, increased uterine volume, ill-defined myometrial heterogeneity, presence of anechoic round myometrial cysts, hyperechoic islands, fan-shaped shadows and/or echogenic subendometrial lines were detected. Focal adenomyosis was diagnosed when foci with adenomyotic characteristics were observed. Main results and the role of chance Clinical pregnancy rate per embryo transfer was 81/167 (48.5%) in those women diagnosed with diffuse adenomyosis versus 23/62 (37.1%) in the focal adenomyosis group (OR = 0.63 95% CI [0.33-1.18], NS). Differences found in clinical miscarriage rate were not statistically significant, being 33/81 (40.7%) for diffuse adenomyosis and 14/23 (60.1%) for the focal adenomyosis group (OR = 2.24 95% CI [0.79-6.63], NS). A lower live birth rate per euploid embryo transfer was observed in women diagnosed with focal adenomyosis, being 9/62 (14.5%) and 48/167 (28.7%) for women who presented diffuse adenomyosis (OR = 0.42 95% CI [0.17-0.95], p=0.027). There were no statistically significant differences between childbirth delivery method (vaginal versus caesarean section). Furthermore, means of gestational age at the time of delivery, newborn size and weight and incidences of low birth weight did not differ between the two groups. Limitations, reasons for caution The retrospective nature of this observational study implies that possible confounders cannot be completely excluded. Also, the accurate diagnostic of adenomyosis is not without complexity and although gynecologists were equally trained to identify direct and indirect markers, different criteria may have been used Wider implications of the findings To our knowledge this is the first study to use an euploid model to assess the impact of the focal versus diffuse nature of adenomyosis in IVF patients. This model permits to correct for numerous covariables attributed to patient’s age and embryo genetic constitution. Trial registration number Not applicable

O-094 Novel stem cell-based twin embryo model reveals inner cell mass division and enhanced endometrial adhesion in monochorionic twin development

Abstract Study question How do monochorionic twin embryos arise and develop during the pre- and peri-implantation stage? Summary answer Twinning involves inner cell mass division during blastocyst expansion and heightened endometrial adhesion, with twin blastoids showing greater implantation potential. What is known already The occurrence of monozygotic twins is between 0.4 and 0.5% of livebirths globally from natural conception, of which the majority are monochorionic. Monochorionic twins are associated with increased risk of complications and higher mortality rates during pregnancy due to twin-to-twin transfusion syndrome, twin anemia-polycythemia sequence, developmental malformations and increased incidence of pregnancy-related diseases in the mother. The rarity of monochorionic twinning, combined with ethical constraints in human embryo research, renders the study of twinning practically infeasible, which presents in a significant knowledge gap regarding the origins and implications of early developmental monochorionic twin embryos development. Study design, size, duration In a stem cell-based model of the blastocyst-stage embryo (i.e., blastoid) conditions were identified that favor the generation of monochorionic twin blastoids. To obtain sufficient statistical power, screening experiments were performed using 3 culture wells per condition, each well containing at least 90 blastoids. Experiments were repeated 3 times and results were pooled. Blastoids were cultured for at least 3 days followed by 2 days on endometrium monolayers on-chip. Participants/materials, setting, methods Human naïve induced pluripotent stem cells and embryonic stem cells were used to form twin blastoids within custom microwell array platforms. Patient-derived endometrium epithelial cells were expanded as organoids and seeded as monolayers in microfluidic chips. Blastoids were infused into the chip, allowed to adhere for 2 days, followed by a controlled stepwise increase of flow rate after which the blastoid adhesion rate to the endometrium layer for both singleton and twin blastoids was quantified. Main results and the role of chance Twin blastoids contained a cystic GATA3+ single layered trophectoderm-like epithelium encasing two distinct inner cell masses (ICMs). Morphological and morphokinetic analyses revealed that twinning occurs during the blastocyst cavitation phase via division of the OCT4+ pluripotent cell mass. After three days of culture, twin blastoids measured 228±32 µm, which is in the upper range of the cyst diameter of a blastocyst. In addition, both sibling ICM-like clusters preserved similar epiblast and hypoblast cell proportions and were consistently positioned nearly 150° (146.6±26°) apart along the blastocoel lining (measured as 2D-projections and in 3D reconstructions), which suggests a minimal angular distance for establishing two separate condensed ICM clusters. Notably, each ICM in twin blastoids contains its own NR2F2+ polar trophectoderm-like region, indicative of implantation readiness. Under defined flow regimes, twin blastoids show increased adhesion capacity to endometrium monolayers compared to singleton blastoids (60% vs 38% at highest flow rate), suggestive of increased implantation potential possibly due to a larger adhesive surface area. Twin blastoids cultured on endometrium monolayers could develop into structures with two distinctive OCT4+ pluripotent cell clumps both delineated by SOX17+ hypoblast-like cells and as a whole encompassed by GATA3+ trophoblast-like cells, suggestive of post-implantation organization. Limitations, reasons for caution While twin blastoids adhered to the endometrium monolayer and maintained two separate OCT4 compartments after 48 hours in post-implantation culture, both singleton and twin blastoids did not establish organized 3D structures associated with later post-implantation development, including amniotic and yolk sac-like cavities. Wider implications of the findings Twin blastoids open new avenues for studying the various aspects of twinning, ranging from their formation processes to the effects of multiple ICMs on trophectoderm maturation and implantation potential. In the future, with more sophisticated endometrium platforms, this model may inform on how clinical complications arise in twin pregnancies. Trial registration number not applicable

P-781 Managing a change of provider bank in a vitrified oocyte donation program

Abstract Study question Does a change in provider bank affect the outcomes of a vitrified oocyte donation program and require laboratory and clinical adjustments? Summary answer In a vitrified oocyte donation program, a change in the provider bank does not affect patients’ outcomes nor require laboratory or clinical adjustments. What is known already Imported vitrified oocyte donation programs are a valuable strategy to provide oocyte donation treatments in settings were donor availability is low or absent. Little is known about how to a change in the provider oocyte bank should be managed in terms of laboratory or clinical adjustments in order not to jeopardize patients’ outcomes. Study design, size, duration Longitudinal cohort study conducted in a Tertiary IVF Center (Centro Scienze Natalità, IRCCS Ospedale San Raffaele, Milan, Italy) between September 2019 and October 2023. Participants/materials, setting, methods All couples undergoing their first imported vitrified oocyte donation cycle were included (n = 235). Oocytes (6 to 9 per cycle) were purchased from one bank (Bank A, Spain, EU) until December 2022 and then from a different bank (Bank B, Spain, EU) from January to October 2023. Single blastocyst-stage embryo transfer policy was adopted in all patients and the cumulative outcomes of patients treated with oocytes purchased from Bank A and Bank B were compared. Main results and the role of chance The number of provided oocytes was higher in Bank B compared to Bank A (8.0 ± 0.8 vs 6.5 ± 0.7, Mean ± SD, p &amp;lt; 0.01). Oocyte survival rates at thawing (87.2 ± 17.2 vs 91.2 ± 16.1 %, Mean ± SD), fertilization rates (75.7 ± 20.8 vs 78.4 ± 28.7, Mean ± SD) and blastulation rates (49.0 ± 28.0 vs 54.5 ± 27.5, Mean ± SD) were stable between Bank A and Bank B respectively, resulting in a higher number of blastocysts available for transfer in cycles performed with oocytes from Bank B compared to Bank A (3.5 ± 2.0 vs 2.4 ± 1.5, Mean ± SD, p &amp;lt; 0.01). Cumulative outcomes showed an improvement in cycles performed with Bank B compared to Bank A (implantation rates 73.8 % vs 62.6 %, ongoing pregnancy rates 69.8 % vs 56.3 %), despite not reaching a statistically significant difference. On multivariate logistic regression, the number of blastocysts available for transfer (OR 2.1, 1.7 -2.7 95% CI, p &amp;lt; 0.01) but not the Bank providing the vitrified oocytes (OR 0.99, 0.40 – 2.43) resulted as significant predictor of ongoing pregnancy. Limitations, reasons for caution Longer follow-up might strengthen our results, as several cycles performed with Bank B are still ongoing and cumulative live-birth rates cannot be currently calculated. In addition, the two banks used are located in the same country. Whether these results also apply to banks located in different settings needs further investigation. Wider implications of the findings Our results reassure about the possibility to manage a vitrified oocyte donation program using oocytes from different banks without jeopardizing patients’ outcomes and without the need for laboratory and clinical adjustments. Trial registration number not applicable