Results Of Cycle Research Articles

P-437 Are serum progesterone levels predictive for reproductive outcomes in artificial cycles if individualized luteal phase support is only administered when progesterone is below 5 ng/ml?

Abstract Study question Do serum progesterone levels predict reproductive outcomes in artificial cycles when individualized luteal phase support is administered only if progesterone falls below 5 ng/ml? Summary answer The low 5 ng/ml progesterone threshold appears to be sufficient for the patient not to require additional progesterone injections when progesterone is above 5 ng/ml. What is known already Serum progesterone (P4) level is negatively associated with ongoing pregnancy rate (OPR) and miscarriage rate in artificially prepared frozen embryo transfer (FET) cycles using standard micronized vaginal progesterone (MVP) for luteal phase support. Individualized luteal support is considered a successful rescue strategy in cycles with low serum progesterone levels eliminating the effect of P4 levels on outcome. Cut-off levels for this rescue strategy range from 8.8 to 10 ng/ml. Study design, size, duration A retrospective single-centre cohort study including a total of 1,016 vitrified-warmed single blastocyst transfers performed at a tertiary fertility centre between October 2021 and December 2022. Blastocysts of ≥ 3CC Gardner score were eligible for vitrification on day 5 or day 6 (Vit-kit or Vit-kit NX, FuijiFilm). Embryos were warmed and subsequently transferred on the same day which was day 5 in the cycle, regardless if the embryo was vitrified on day 5 or day 6. Participants/materials, setting, methods We included 595 patients undergoing an artificially prepared embryo transfer (ET) cycle using MVP 800mg BID for luteal phase support. Serum P4 levels were determined on the day of ET with the initiation of additional injections of subcutaneous P4 from the day after ET in patients with P4 < 5ng/ml. Primary endpoint was OPR. Multivariable logistic regression was performed to correct for confounders. Generalized estimating equations (GEE) models were fitted for primary and secondary outcomes. Main results and the role of chance OPR was comparable for the 3 groups: 9/40 (22.5%) for patients with P4 <5ng/ml, 64/275 (23.3%) for patients with P4 5-10 ng/ml and 181/701 (25.8%) for patients with P4 >10ng/ml (p = 0.377). No significant association between P4 category and likelihood for OPR was found after adjusting for confounders. Early clinical miscarriage rate was significantly different between the 3 groups: 5/40 (12.5%) in patients with P4 <5ng/ml, 26/275 (9.5%) with P4 5-10ng/ml and 37/701 (5.3%) with P4 >10ng/ml (P = 0.005). Limitations, reasons for caution Higher clinical miscarriage rate in cycles with a P4 level under 10 ng/ml questions the efficacy of rescue progesterone in cycles with a low P4. The patient population also exists of a subgroup of PGT-a tested cycles which was not included as a potential confounder in this analysis. Wider implications of the findings The 5 ng/ml P4 threshold appears to be sufficient for the patient not to require additional P4 injections when P4 is above 5 ng/ml. Consequently, a significantly lower proportion of cycles would need to be supplemented with rescue progesterone; 3.8% versus 31.3% for the 10 ng/mL cut off. Trial registration number ONZ-2023-0223

P-254 Optimizing clinical outcomes in failed ICSI Donor cycles: evaluating the efficacy of Assisted Oocyte Activation

Abstract Study question Does Assisted Oocyte Activation (AOA) confer benefits to couples undergoing donor ICSI cycles with a history of poor clinical outcomes and poor sperm quality? Summary answer AOA demonstrates efficacy in enhancing reproductive outcomes in donor ICSI cycles, in cases where oocyte activation deficiency (OAD) is attributed to a sperm factor. What is known already Oocyte activation is a spatial-temporal process caused by a series of intracellular calcium oscillations (Ca2+)triggered by the entry of sperm into the oocyte. Insufficient Ca2+ oscillations, primarily attributed to the absence of sperm-specific phospholipase C zeta (PLCζ) can result in OAD that leads to unsuccessful fertilization and poor embryo growth. Ionomycin and calcimycin, are the most common activating agents used to restart meiosis by raising intercellular Ca2+. As far as our knowledge extends, there aren’t studies reporting clinical outcomes on the use of AOA in patients who undergo cycles both without and with this treatment in donor oocytes. Study design, size, duration This study includes 38 couples undergoing ICSI cycles with donor oocytes from January 2020 to December 2023. After a previous cycle with a fertilization rate of < 50% and poor clinical outcomes, these couples underwent a subsequent attempt with AOA. Maternal age of recipients was 42±4.7 and 42±5 years in cycles without and with AOA (P=NS). Fertilization, blastocyst quality, implantation, clinical pregnancy rates (CPR) and pregnancy loss were compared between the cycles with and without AOA. Participants/materials, setting, methods Oocytes were exposed to a ready-to-use solution of Ca2+-ionophore A23187 (GM508 Cult-Active, Gynemed, Germany) for 15 min after sperm injection. Embryos were cultured in a time-lapse technology (Geri®) andevaluated according to the Gardner blastocyst grading system. Embryo transfer was performed on Day 5 or Day 6. Vitrified and fresh ejaculated sperm samples were used. T-test and Fisher’s Exact test were used for statistical analysis. P-value was considered statistically significant at a threshold of < 0.05. Main results and the role of chance A total of 38 men underwent ICSI cycles alongside their female partners, utilizing donor oocytes. The men’s average semen parameters were as follows: concentration of 15.3±25 x 106/mL, motility of 20.1±15%, and 2.0±1% morphology. In the initial 41 cycles without the AOA procedure, an average and standard deviation of 5.8±3 donor oocytes were injected, resulting in a fertilization rate of 33.9% (81/239) and a blastocyst rate of 30.8% (25/81). Among these cryopreserved embryos, 72% (18/25) were identified as top-quality, characterized by A and/or B quality of both inner cell mass and trophectoderm. Couples (N = 13) who underwent a transfer had an implantation rate of 19% (4/21), with CPR of 28.5% (4/14), which resulted in a pregnancy loss of 75% (3/4). Subsequently, these couples underwent 47 ICSI cycles with AOA, injecting an average of 5±1.7 donor oocytes (P=NS). This led to a significantly higher fertilization rate of 74.2% (176/237, P < 0.0001) and a blastocyst rate of 51.7% (91/176, P < 0.01), with 61% (56/91) identified as top-quality embryos (P=NS). Couples (N = 31) who underwent a transfer had a notable increase in implantation rate to 52% (25/48, P < 0.05), accompanied by a significant rise in CPR, reaching 71.4% (25/35, P < 0.01). Importantly, pregnancy loss decreased to 26% (6/23, P=NS). Limitations, reasons for caution The number of patients included in this study is limited. Although we excluded that OAD could be oocyte-related by using donor gamete, PLCζ or mouse oocyte activation tests were not performed to confirm sperm-related OAD. All patients, diagnosed with teratozoospermia, likely exhibit abnormalities causing PLCζlocalization issues or its absence. Wider implications of the findings In our study, sperm’s inability to generate accurate calcium signaling pathways correlates with poor clinical outcomes, even with donor oocytes. Consequently, for couples facing Oocyte Activation Deficiency attributed to sperm factors, implementing the AOA procedure significantly improves fertilization, blastocyst formation, implantation, and clinical pregnancy rates. Trial registration number na

P-229 Effect of morula pattern on clinical outcomes in single vitrified-warmed blastocyst transfer cycles

Abstract Study question Does morula pattern affect clinical outcomes in single vitrified-warmed blastocyst transfer cycles? Summary answer Ongoing pregnancy rate is statistically increased when transferring the blastocyst derived from fully compacted morula in single vitrified-warmed blastocyst transfer cycles. What is known already Time-lapse microscopy has enabled the detailed identification and measurement of dynamic events of embryo development. Recent studies have shown that the exclusion of one or more cells from the compacted morula is associated with reduced developmental competence and a decrease in pregnancy rate. Additionally, it is also associated with decreased rates of PGT-A euploid and implantation. These findings demonstrate the correlation between morula pattern and the outcomes of assisted reproductive technologies. Study design, size, duration A retrospective cohort study was performed between January 2020 and November 2023. A total of 99 single vitrified-warmed blastocyst transfer cycles (women ≥ 35 years) were analyzed. The rates of biochemical pregnancy, clinical pregnancy, implantation, miscarriage, and ongoing pregnancy were evaluated. Participants/materials, setting, methods Images of morula stage embryos were collected at 7-focal planes and every 5-minute interval using a time-lapse microscope. The morula stage embryos were divided into two groups according to their compaction patterns. Morula stage embryos without excluded or extruded cells were defined as fully compacted morula (FCM, n = 47). In contrast, Morula stage embryos with excluded or extruded cells were defined as partially compacted morula (PCM, n = 52). Main results and the role of chance There were no differences of patient characteristics between FCM and PCM regarding female age (37.8 ± 2.1 vs. 37.8 ± 1.8, p = 0.96), number of previous IVF failure (0.5 ± 1.1 vs. 0.9 ± 1.6, p = 0.23), number of retrieved oocytes (16.1 ± 4.0 vs. 14.3 ± 5.1, p = 0.14), maturation rate (86.5% vs. 89.1%, p = 0.18), fertilization rate (73.8% vs. 69.9%, p = 0.39), survival rate (100% vs. 100%, p = Not applicable), and number of transferred embryos (1.0 ± 0.0 vs. 1.0 ± 0.0, p = Not applicable), with the exception of rate of good-quality embryos on Day 3 (44.7% vs. 37.6%, p = 0.04). No statistical differences were observed in rates of biochemical pregnancy (44.7% vs. 34.6%, p = 0.31), clinical pregnancy (40.4% vs. 26.9%, p = 0.15), miscarriage (11.4% vs. 15.4, p = 0.57), and implantation (40.4% vs. 26.9%, p = 0.15) between FCM and PCM, respectively. However, FCM demonstrated a significantly increased ongoing pregnancy rate compared to PCM (29.8% vs. 11.5%, p = 0.02). Limitations, reasons for caution This study was conducted with a small sample size, which limited the generalizability of the findings. Therefore, further studies are needed with a larger sample size and more diverse populations to confirm our findings. Wider implications of the findings The compaction pattern of morula stage embryos can be an indicator for embryo selection. The blastocyst derived from fully compacted morula has the potential to improve ongoing pregnancy rate in single vitrified-warmed blastocyst transfer cycles. Trial registration number not applicable

P-153 Optimizing clinical outcomes in single vitrified-thawed blastocyst transfer cycles: impact of blastocyst re-expansion status

Abstract Study question is the blastocyst re-expansion status according to the thawing-transfer time interval related to the clinical outcomes in a single frozen-thawed blastocyst transfer cycles? Summary answer The post-thawing blastocyst shrinkage is linked to lower clinical outcomes, and minimizing the time between thawing and transfer optimizes outcomes especially for shrunken blastocysts. What is known already • A reduced ART outcome was observed with the use of shrunken post-warming blastocysts (Ito et al., 2023) • The spontaneous blastocyst shrinkage observed during in vitro embryonic development is considered as a negative prognosis factor for implantation (Sciorio et al., 2020) • The blastocyst’s re-expansion level after thawing proves to be the best post-thaw parameter for the prediction of live birth (The Vienna consensus., 2017. Ahlstrom et al., 2013). • The fast blastocele re-expansion seems to have a predictive value for implantation in frozen-thawed blastocyst transfer cycle (Shu et al., 2009). Study design, size, duration This was a retrospective study of 577 single frozen-thawed blastocyst transfer cycles from January 2022 to April 2023. Participants/materials, setting, methods Only B4 and B5 blastocyst quality obtained in day-5 were included in this study. The morphological characteristics were evaluated: after thawing (T0) and at Transfer time (TR). Blastocysts with 50% reduction of blastocele were classified “Shrunken”, the rest are “re-expanded”. and categorized into Group-1: re-expanded at T0 (n = 173); Group-2: shrunken at T0 and re-expanded at TR (n = 135); Group-3: shrunken at T0 and TR (n = 199). Statistical tests: chi-square, T-test and Mann-Whitney. (Statistical significance p < 0.05*). Main results and the role of chance Clinical outcomes of re-expanded blastocysts comparing to shrunken blastocysts at TR were respectively 42.21% versus 32.71% for pregnancy rate (PR) (p < 0.007),39.61% versus 30.48% for implantation rate (IR) (p < 0.02) and 35.71% versus 22.30% for life birth rate (LBR) (p < 0.004), a significantly higher outcomes were observed for re-expanded blastocysts. The miscarriage rate decreased from 25.00% to 9.23% (p < 0.001). The transfer of shrunken blastocysts in an interval of time within 1 hour or less comparing to more than 1 hour between T0 and TR showed the following results: PR = 40.82% versus 28.07% (p < 0.032), IR = 39.81% to 25.10%, (p < 0.02) and LBR = 26.53% versus 19.88% (p < 0.2). a significantly higher clinical outcomes were observed for shrunken blastocysts transferred within 1 hour or less. Group analysis: the PR, IR and LBR significantly increased for Group-1 comparing to Group 2. For Group-3, shrunken blastocysts at TR had the lower outcomes. (respectively p = 0.003; 0.017; 0.0002) Limitations, reasons for caution It is an ongoing retrospective observational study. Blastocysts with a low quality (B3 or less) were excluded from this study how limit our ability to extend the findings to low morphology degrees not covered by this research. Wider implications of the findings The management of frozen blastocyst transfers in IVF laboratories have to take into consideration in addition to the classic morphological evaluation, the blastocoele re-expansion state and the time interval between thawing and transfer to optimize the transfer outcomes. Trial registration number not applicable

P-391 Association between meteorological season at the time of embryo transfer and pregnancy outcomes in freeze-all cycles: lessons from seasonal reproductive mammals

Abstract Study question Is there any effect of meteorological season at the time of embryo transfer on clinical outcomes of freeze-all cycles? Summary answer Optimal conditions for implantation appear to be associated with spring and summer. Embryo transfers performed in autumn or winter are associated with reduced ongoing pregnancy. What is known already Extensive research has consistently shown that most mammals are seasonal breeders, and as day length increases, gonadotropin secretion increases, to anticipate reproduction in the spring and summer months. There is intriguing evidence that there is a seasonal variance in human reproduction, but the data are inconclusive. Therefore, the goal for the present study was to evaluate the effect the meteorological season at the time of embryo transfer on clinical outcomes of freeze-all cycles. Study design, size, duration This historical cohort study was performed in a private university-affiliated IVF center between February 2018 and December 2022. A total of 4952 frozen-thawed embryos transferred to 3725 cycles in a single clinic were analyzed. Participants/materials, setting, methods Both vitrification and the warming procedures were performed using the Cryotop method. Embryos survival and clinical outcomes were analyzed by the season, at the time of embryo transfer, using generalized linear models adjusted for potential confounders. Main results and the role of chance The mean maternal age was 37.0 ± 4.7 years. Embryos were cryopreserved for a mean of 8.1 ± 17.3 months. Autumn was designated as the reference season for all analyses. No significant differences were observed in embryo survival rates when the seasons were compared, however, lowest implantation and pregnancy rates were observed when embryo transfers occurred in autumn (44.6%), followed by winter (45.8%, OR: 1.049, CI: 0.876 – 1.257, p = 0.603) and summer (49.0%, OR: 1.196, CI: 1.010 – 1.415, p = 0.038), while spring embryo transfers had a 30% increased odds of pregnancy (51.2%, OR: 1.302, CI: 1.100 – 1.541, p = 0.002). An increased miscarriage rate was observed when embryo transfers occurred in autumn (13.9%), followed by winter (11.4%, OR: 0.510, CI: 0.323 – 0.805, p = 0.004) and summer (10.4%, OR: 0.461, CI: 0.292 – 0.727, p = 0.001), while spring embryo transfers had a 63% decreased odds of miscarriage (5.6%, OR: 0.369, CI: 0.230 – 0.592, p < 0.001). Limitations, reasons for caution The use of historical cohort groups is a drawback. Despite the eligibility criteria for inclusion in the analysis, potential differences in the baseline characteristics cannot be ruled out. Wider implications of the findings In seasonal breeding mammals, melatonin increases the gonadotropins’ release during the transition period. Melatonin rise favors embryo implantation and protects offspring by increasing progesterone levels. Our evidence suggests that human reproductive potential may be influenced by climatic variations. Trial registration number N/A

P-663 Comparing clinical outcomes in PGT-A cycles using donated oocytes between progesterone and GnRH-antagonist protocols

Abstract Study question Does Progesterone Primed Ovarian Stimulation (PPOS) demonstrate comparable efficiency to the GnRH-antagonist protocol in terms of laboratory/reproductive outcomes in PGT-A cycles with donated oocytes? Summary answer PPOS demonstrates efficiency in PGT-A cycles with donated oocytes, comparable to the GnRH-antagonist protocol, providing cost-effectiveness and enhanced donor comfort. What is known already The demand for TRA cycles with donated oocytes steadily rises each year. This treatment instills high hopes for success. Ongoing advancements in donor stimulation protocols prioritize safety and comfort. The shift from LH agonist to antagonist suppresses LH peaks, and recently, PPOS has joined, offering a more comfortable, cost-effective, and equally safe alternative with fewer ultrasound checks, mitigating ovarian hyperstimulation syndrome. Study design, size, duration Retrospective assessment of an oocyte donor cohort undergoing ovarian stimulation: 182 cycles with the GnRH-antagonist protocol (Group 1: G1) and 120 with PPOS (Group 2: G2), conducted between July 2017 and June 2023. Ovarian stimulation involved 225 IU/d of FSHr or FSHu, triggering with a GnRH agonist, and subsequent biopsy of evolutionarily robust embryos after extended culture. Both fresh and vitrified oocytes, inseminated with either self or donor sperm, were included. Participants/materials, setting, methods We analyzed 1188 embryos (G1: 676; G2: 512). Trophoectoderm biopsies from D5/D6 blastocysts underwent NGS using the Illumina platform (VeriSeq Illumina®, San Diego, CA, USA). Comparison included total and MII oocyte numbers, fertilization rates, viable embryos, euploid/aneuploid embryos, mosaic embryos, and clinical outcomes: biochemical pregnancy (BPR), biochemical pregnancy loss (BPLR), clinical pregnancy (CPR), early pregnancy loss (EPLR), ongoing pregnancy (OPR), and live birth (LBR) rates. Statistical analyses were carried out using R statistical software (v.4.3.1). Main results and the role of chance The mean ages of donors (25.57±4.05) and recipients (41.82±4.06) were comparable in both groups. The male partner’s age differed (G1: 40.47±7.87; G2: 42.34±7.65) (p = 0.019). Results were adjusted for confounding factors, including recipient and donor ages, oocyte and seminal origin, and male factor variables. Ovarian stimulation duration (9.26 days), total gonadotropin dose (2015.64 IU), and oocyte origin (fresh G1: 69.8 %; G2: 62.5 %; vitrified G1: 30.2 %; G2: 37.5 %) showed equivalence. Statistical significance emerged in total oocytes retrieved (G1: 17.92±7.64; G2: 20.23±7.89) (p = 0.008), mean microinjected MII (G1: 10.25±1.79; G2: 10.07±1.36) (p = 0.040) and fertilization rate (G1: 73.98 %; G2: 79.44 %) (p = 0.001). The usable embryo rate was similar (G1: 54.78 %; G2: 54.47 %). Significant differences arose in mean biopsied embryos/cycle (G1: 3.71; G2: 4.27) (p = 0.016), but not for aneuploid embryos (G1: 29.71 %; G2: 29.49 %) (p = 0,998). Biochemical pregnancy rates were significant (G1: 48.8 %, G2: 60.4 %) (p = 0.022). Other clinical parameters showed no differences, with LBR at 35.5 % in G1 and 37.8 % in G2 (p = 0.752). Limitations, reasons for caution The study is retrospective, where we addressed potential biases by incorporating confounding variables. However, to confirm our initial findings, randomized prospective studies with an appropriate sample size are essential. Wider implications of the findings In egg donation cycles, PPOS shows optimal embryonic performance resulting in a live birth rate comparable to the GnRH antagonist protocol. Additionally, it offers cost-effectiveness and enhanced comfort for donors. Trial registration number Not applicable

P-293 Influence of the endometrial microbiota composition on the clinical outcomes of egg donation PGT-A cycles with controlled endometrial receptivity

Abstract Study question Does the endometrial microbiota composition and diversity influence embryo implantation and pregnancy evolution in assisted reproduction treatment (ART) cycles? Summary answer Endometrial microbiota composition influences ART success. Detection of endometrial pathogens is associated with poor outcomes whereas sterile endometria show the highest pregnancy and live-birth rates What is known already The endometrial microbiota has emerged as a possible influencing factor in the results of ART. Recent research suggests its impact on female reproductive health, particularly in patients with chronic endometritis (CE), where the presence of microbial pathogens associated with this condition has been linked to infertility. In turn, the bioregulatory role of species of Lactobacillus in this tissue has been explored, although its essentiality or benefit for female reproductive function continues to be topics of debate. Study design, size, duration This is a case-control retrospective study analysing for the first time the influence of the endometrial microbiota composition on the clinical outcomes of 220 women undergoing egg donation cycles with Preimplantation Genetic Testing for Aneuploidy (PGT-A) and controlled endometrial receptivity between March 2016 and April 2021 in IVF-Life Alicante (Spain). ART results after the transfer of a single euploid blastocyst in the WOI of patients with different endometrial microbiota profiles were analysed and compared. Participants/materials, setting, methods Presence of 18 microbial CE pathogens and 4 Lactobacillus species was determined by high-throughput qPCR (MicrobioMap®, iGLS) in endometrial samples obtained during the WOI of a hormone replacement therapy cycle. In all cases, PGT-A by next generation sequencing (NGS) (EmbryoMap, Vitrolife) and study of endometrial receptivity by gene expression analysis (ER Map, iGLS) were performed. Clinical outcomes (β-hCG+, β+ and live birth, LB) in relation to the endometrial microbiota profile were analysed and compared. Main results and the role of chance In the study, 31.8% of patientś endometria were identified without microbial detection, 40% exclusively with Lactobacillus, 13.2% with pathogens only, and 15% with both. Clinical results revealed significant differences in β+ rates among the groups (p < 0.05). The absence of microorganisms was associated with higher success rates (β + 72.9%), while the presence of pathogens significantly reduced pregnancy success (β + 41.4%). A similar trend was observed in LB rates, although it did not reach statistical significance (44.3% and 24.1%, respectively). The presence of Lactobacillus alongside pathogens improved clinical outcomes (β + 57.6% LB 48.5%). Interestingly, exclusive presence of Lactobacillus showed lower implantation rates than patients without microbial detection (β + 58%). These findings highlight the impact of microbial composition on the clinical outcomes of ART cycles, underlining the association between endometrial microbiota patterns and pregnancy success. Limitations, reasons for caution This study is constrained by its retrospective nature, emphasizing the need for further validation through randomized controlled trials, non-selection studies, or other investigative approaches to confirm the extent of any clinical benefits. Endometrial biopsies were obtained transcervically, while executed with utmost care, risk of contamination cannot be completely excluded. Wider implications of the findings The composition and diversity of the endometrial microbiota is key for ART success. A sterile endometrial environment offers optimal conditions for implantation and pregnancy. The study highlights the potential of Lactobacillus in counteracting the negative impact of pathogenic presence. Trial registration number not applicable

P-639 Are GnRH-agonists (GnRH-a) safer and more effective ovulation triggers than human chorionic gonadotrophin (hCG)? A retrospective analysis of frozen embryo replacement cycle (FERC) outcomes

Abstract Study question Are GnRH-agonists (GnRH-a) safer and more effective ovulation triggers than human chorionic gonadotrophin (hCG)? A retrospective analysis of frozen embryo replacement cycle (FERC) outcomes Summary answer GnRH-a trigger reduces the incidence and severity of ovarian hyperstimulation syndrome (OHSS) leading to significantly improved clinical outcomes when compared to hCG trigger for FERCs. What is known already Ovulation induction plays a crucial role in the success and safety of ART cycles. hCG is extensively used as an alternative to LH to trigger ovulation. However, high levels of sustained hCG exposure increases the risk of OHSS, a potentially life-threatening complication of ART. To eliminate the risk and incidence of OHSS, GnRH-a can be used to trigger ovulation. Although there are concerns regarding clinical outcomes with fresh transfers following GnRH-a trigger, it elicits a more physiological response compared to hCG. This may lead to improved embryo quality, utilisation, and better clinical outcomes following a freeze-all strategy, reducing patients’ time-to-pregnancy. Study design, size, duration This was a retrospective data analysis of FERC outcomes following fresh IVF or ICSI cycles, involving ovulation induction using either hCG or GnRH-a as a final trigger. The evaluation included results from cycles spanning an eight-year period, from January 2012 to December 2019 at Hammersmith Hospital London. A total of 160 cycles were included in the study, with 76 in the hCG trigger group and 84 in the GnRH-a trigger group. Participants/materials, setting, methods Strict inclusion criteria were employed to render the study groups as comparable as possible and to minimise the effect of independent variables, such as oocyte and sperm factors, on oocyte or embryo developmental competence. Inclusion criteria: women ≤37 years old at the start of treatment, GnRH antagonist stimulation, blastocyst vitrification-warming and transfers only. Statistical significance was calculated using independent t-test and Fisher’s Chi-square exact test. Main results and the role of chance The mean age (±SD) of patients at the time of oocyte retrieval was comparable across groups. The average number of oocytes collected were significantly higher in the GnRH-a group compared to hCG (28.31 vs. 18.07, respectively, P < 0.001). Embryological data (maturation, fertilisation, blastocyst formation, blastocyst utilisation and good quality blastocyst formation rates) were comparable across both groups. OHSS rate was significantly lower in the GnRH-a group (17% vs. 50%. P < 0.0001). The following clinical data were significantly higher (P < 0.05) in the GnRH-a group compared to hCG: implantation rate (56% vs. 36%), clinical pregnancy rate (56% vs. 36%) and live birth rate (42% vs. 27%). Limitations, reasons for caution The biggest limitation of this study is its retrospective nature and the application of various inclusion-exclusion criteria that have resulted in relatively small sample sizes. Additionally, numerous other confounders, e.g. patient body mass index, cause/duration of infertility and stimulation duration, have not been considered in this study. Wider implications of the findings The findings of this study are promising and demonstrate a great potential for benefit in the use of GnRH-a trigger with a freeze-all strategy to minimise the risk of OHSS, diminishing the associated patient morbidity and mortality, reducing healthcare costs, improving clinical outcomes, and reducing the overall time-to-pregnancy for patients. Trial registration number not applicable

P-755 Effect of female age and specific cycle characteristics on success in modified natural frozen-thawed single euploid embryo transfer cycles (mNC/FET)

Abstract Study question Does the age of woman and specific cycle characteristics impact the success of modified natural frozen-thawed single euploid embryo transfer cycles (mNC/FET)? Summary answer The success rate of mNC/FET cycles is similar in all age groups. As the LH level increased ( above 23.5ng/dL) the success was significantly increased. What is known already The success of frozen embryo transfer can depend on various factors such as the patient’s age, the number of transferred embryos, the duration of embryo culture, and the method used to prepare the endometrium (Holschbach et al. 2023). However, there is currently insufficient evidence in the literature about the effect of age and cycle characteristics on the effectiveness of mNC/FET cycles in patients who have received single top and good quality euploid embryos. Study design, size, duration This study, conducted at Istanbul Memorial Hospital, ART and Reproductive Genetics Center, is a retrospective, single-centre analysis of 583 cycles of euploid mNC/FET in women aged 22-44 years. The study period was from July 2017 to January 2024. The cycles were divided into two groups based on the age of the women. Group A (n = 408) included women under the age of 38, while Group B (n = 175) included women aged 38 or above. Participants/materials, setting, methods The study investigated success predictors in mNC/FET with top and good-quality embryos. Excluded were women with recurrent pregnancy losses, recurrent implantation failure, high BMI (>35kg/m2), uterine/endometrial problems, severe male infertility, and autoimmune diseases. The mNC/FET success was a pregnancy lasting 12 weeks or more. The analysis included patient demographics and cycle outcomes. Chi-square, t-tests, and Mann-Whitney U tests assessed variables with a p-value < 0.005, indicating statistical significance. Main results and the role of chance No significant demographic differences were observed between the two groups, except for AMH levels. AMH levels were significantly higher in younger group than older group (3.02 ng/ml vs. 1.96 ng/ml, p = 0.000). The mNC/FET success rates were similar, with 76% in the younger group and 73% in the older group. Estradiol levels the day before trigger day were significantly higher in older group (278.02 pg/ml vs. 237.84pg/ml, p = 0.028). Both groups had similar mean LH levels (32.50 IU/L and 32.41 IU/L, respectively), estradiol levels and endometrial thickness on the trigger day. In the younger group, LH rise was observed later, follicular phase was longer, and embryo transfer day was later than the older group (p = 0.001). Univariate regression analysis revealed that increased LH level was an important independent variable in achieving mNC/FET success, with a 1.001-fold increase (p = 0.043). The LH levels of 23.5 IU/L or higher predicted high mNC/FET success with 60% sensitivity and 43% specificity based on the Receiver Operating Characteristic curve. (AUC: 0.606, %95 CI 0.540-0.671, p = 0.002). Prolonged infertility duration and previous ET failures reduced mNC/FET success by 0.889 and 0.544-fold, respectively (p = 0.002, p < 0.001). Higher β-hCG levels on days 14 and 16 increased mNC/FET success by 1.038-fold and 1.008-fold, respectively (p < 0.001). Limitations, reasons for caution Our study has limitations as it was retrospective. Prospective randomized studies are needed to evaluate the differences between the young (age <38) and old patient groups (age ≥38) based on mNC/FET success. The association between LH rise and mNC/FET success needs verification with a larger sample. Wider implications of the findings The mNC/FET success rates are similar in young (age <38) and old patient groups (age ≥38). However, prolonged infertility duration and previous failed ET cycles decreased the success of mNC/FET. Additionally, It is important to schedule trigger time after the optimum LH rise, which is 23.5 IU/L or higher. Trial registration number not applicable

P-750 Is maximalization of the ovum pick-up (OPU) procedure beneficial for the outcome of assisted reproductive technology (ART) cycles?

Abstract Study question Is aspiration of more oocytes than the antral follicle count (AFC) beneficial for the current (pregnancy/live birth rates) and future products of an ART cycle? Summary answer Aspirating more oocytes than the AFC does not influence the outcome of the fresh cycle but is beneficial for fertility preservation and cumulative pregnancy rates. What is known already AFC is a reliable and immediate indicator for ovarian reserve assessment and is in correlation with the ovarian response to gonadotropin stimulation. Additionally, correlation between AFC and embryo quality, clinical pregnancy and live birth rates was reported. There is no data concerning the impact of the ratio between the AFC and actual number of oocytes retrieved on cycle outcome. Study design, size, duration Data of the first oocyte aspiration for ICSI performed between 2018-2022 in attempt to conceive (ICSI, n = 399) or for planned oocyte vitrification (fertility preservation FP, n = 283) was retrieved. Each group was divided into two subgroups according to their ‘oocyte/AFC index’ (OAFCI): <1 and ≥1. The stimulation parameters, number of aspirated oocytes, their maturity rate, number of cryopreserved oocytes/embryos, clinical pregnancy (CPR) and live birth rates (LBR) were compared between the subgroups. Participants/materials, setting, methods The AFC was determined by professional sonographers using a 9 MHz transvaginal ultrasound probe. The most adjacent measurement to the stimulation initiation was used. Stimulation protocol and FSH dose were determined according to the AFC and individual clinical consideration. Patients not in their first cycle, natural cycle aspirations, and cases in which no oocytes were retrieved, were excluded. Main results and the role of chance OAFC≥1 was associated with higher pre-trigger estradiol (6159 pmol/L vs. 4304, p < 0.001 for ICSI, 4949 vs. 3488, p < 0.001 for FP), and longer duration of simulation (9.8 days vs. 9, p < 0.001 for both FP and ICSI). More oocytes were aspirated in OAFC≥1 groups in both FP (16.9±11.2 vs. 7.9±5.9, p < 0.001) and ICSI (17.4±9.8 vs. 10.7±6.7, p < 0.001). Oocyte maturity was unaffected by the OAFCI in the ICSI group, but was lower in FP group at OAFC≥1 (0.79 vs.0.84 p = 0.005). OAFCI≥1 was associated with a higher number of cryopreserved embryos (3.9 vs. 2.3, p < 0.001 for ICSI) and a higher number of vitrified oocytes (13.4 vs. 6.4 p < 0.001 for FP). The OAFCI had no impact on CPR (39% vs. 60%, p = 0.27) and LBR (19.9% vs. 24.8%, p = 0.33). On multivariate analysis controlling for age, gonadotropin dosage and duration of stimulation, OAFC≥1 was associated with a higher number of cryopreserved embryos (ICSI group aOR 1.2, 95% CI 1.1-1.3, p < 0.001), and vitrified oocytes (aOR 1.2, 95% CI 1.1-1.2, p < 0.001) and lower maturity index (aOR 0.1, 95% CI 0.03-0.51, p < 0.001) in the FP group. Limitations, reasons for caution Retrospective study analyzing results of treatment cycles without an intention to aspirate differently. Wider implications of the findings Aspiration of a more oocytes than the current AFC was not associated with higher CPR or LBR in the fresh cycle, but harbors the possibility to cryopreserve more oocytes and embryos. This might translate into higher cumulative pregnancy rates later on. Trial registration number Not applicable

P-683 Progestins vs flexible GnRH antagonist for LH suppression during controlled ovarian stimulation in POSEIDON groups 3 and 4 patients: Analysis of effectiveness and cycle outcomes

Abstract Study question How do cycle outcomes differ between controlled ovarian stimulations using progestins vs flexible GnRH antagonists for LH suppression in women with diminished ovarian reserve (DOR)? Summary answer While progestin use is associated with significantly higher blastocyst rate than GnRH antagonists in POSEIDON group 4, the latter gives better results in group 3. What is known already Controlled ovarian stimulation (COS) in patients with DOR carries the additional risk of premature luteinizing hormone (LH) surge and ovulation.GnRH antagonists are popular for LH suppression in COS because of their convenient, quicker onset of action, flexibility to use GnRH agonist as a trigger and continue as double stimulation, allowing rapid pooling of embryos. Ease of oral administration, combined with cost-effectiveness and retention of all the benefits of GnRH antagonists makes progestins an attractive alternative to GnRH antagonists for COS in patients with DOR who often need multiple stimulation cycles to enable the pooling of embryos. Study design, size, duration An open-label, multicentric, randomized controlled study was conducted over 1 year from January 2023 to December 2023. 140 women aged 21- 42 years and with AMH <1.2 ng/dl were randomized into 2 groups in a 1:1 ratio, using either oral progestins or GnRH antagonists for LH suppression. The two groups were further comparative analyzed under POSEIDON 3 and 4 subgroups. Those with BMI >40kg/m2 and with partners having severely compromised semen parameters were excluded. Participants/materials, setting, methods In Group A (PPOS): Medroxyprogesterone acetate 10 mg orally was given daily with gonadotropins (hMG 300- 375 IU) from cycle day 2 until trigger. In Group B (Antagonist), patients had daily GnRH antagonist, cetrotide 0.25 mg, subcutaneous administration started when the dominant follicles reached 12-14 mm size during controlled ovarian stimulation. This was continued until the trigger. Following oocyte retrieval and ICSI, embryos were cultured until D5 and vitrified fortransfer in subsequent HRT cycles. Main results and the role of chance Patients in Group A, using PPOS, were noted to have significantly better fertilization rates than those in Group B, using flexible GnRH antagonists (0.82 + 0.2 vs 0.66 + 0.4, p-value <0.01). Though the number of top-quality embryos (TQE) frozen was not significantly different between groups A and B (p-value = 0.44), a significant difference in the outcome was noted when comparatively analyzed under the subgroups of POSEIDON groups 3 and 4. While patients in POSEIDON group 4 got significantly more top-quality embryos (TQE) when progestins were used for LH suppression (1 + 0.11 vs 0.77 + 0.41, p-value <0.01), those in POSEIDON group 3 got significantly more top-quality embryos when GnRH antagonist was used (0.94 vs 2, p-value <0.01). Patients in Group A and B were found to have no significant difference in the following outcomes: incidence of premature LH surge (4.3% vs 7.1%, p value= 0.71), number of days of stimulation (10.26 + 2.18 vs 10.26 +2.94, p value= 0.99), total gonadotropin dosage used (3448.64+ 1007.98 vs 3087.41 + 1260.56, p value=0.06), total number of oocytes retrieved (5.84 + 3.3 vs 4.9 + 3.4, p value=0.09) and total cycle cancellation rate (30.1% vs 35.7%, p value= 0.11). Limitations, reasons for caution The small sample size of the cases limits the current statistical power of the study. The results being encouraging need to be confirmed in a larger patient population and followed for a longer duration to enable calculation of implantation and clinical pregnancy rates for all patients. Wider implications of the findings Oral progestins are an effective and cheaper, patient-friendly alternative to injectable GnRH antagonists during COS in women with DOR. Considering the significantly higher TQEs formed, PPOS can be preferred in older, POSEIDON group 4 patients, whereas flexible GnRH antagonist protocol can be our choice in the younger, POSEIDON group 3. Trial registration number Not applicable

P-768 Is it time for a consensus on key performance indicators for cycles involving donation and surrogacy?

Abstract Study question As there are no agreed standards for bench marking in cycles involving donation and surrogacy, how do we measure performance for these treatment types? Summary answer Until an international consensus is undertaken, we must define benchmarks using both in-house and published data from the Human Fertilisation and Embryology Authority (HFEA) register. What is known already Treatment cycles involving donor gametes or surrogacy have increased exponentially in recent years (Horsey, 2023; HFEA, 2020). Key performance indicators (KPIs) are critical for monitoring treatment effectiveness and safety. The Vienna Consensus (2017) is the accepted standard against which clinics should measure performance. However, the publication does not include data on cycles involving donation and surrogacy. In the absence of agreed standards, it is difficult for clinics to measure efficacy for these patient groups. Defining benchmarks for such cohorts is particularly challenging as the gametes used in donation and surrogacy treatment types may come from both fertile and sub-fertile populations. Study design, size, duration Retrospective analysis of anonymised United Kingdom (UK) data, published by the HFEA, from 2014 to 2018, was performed. Outcomes for 26290 donor intrauterine insemination (DIUI), 12262 in vitro fertilisation (IVF), 11341 intracytoplasmic sperm injection (ICSI) and 12453 frozen embryo transfer (FET) cycles, all using donor gametes, were included in this study. In cycles where surrogacy was indicated, gamete origin could not be determined, preventing the data from being included in this study. Participants/materials, setting, methods Using the complete HFEA data set, the average live birth rate, for each treatment type (excluding surrogacy), was calculated. This average was considered the target benchmark when comparing the average live birth rates at the clinic. Each quarter, a rolling 12 months of in-house retrospective data was used to assess clinic performance. Warning and action limits were set using standard deviations calculated using the 5 averages obtained from each year of HFEA data included. Main results and the role of chance The average live birth rates determined using the HFEA data, to be used as benchmarks for performance, were as follows; DIUI (13.7%), IVF (42%), ICSI (37%) and FET (36%). It is noteworthy that live birth rates reported by the HFEA were per embryo transfer (ET), rather than per embryo, meaning more than one live birth could be reported per ET. Discrepancies in outcome reporting meant that the national clinical pregnancy rate could not be determined for all treatment types, nor could fertilisation rate. Therefore, the clinic used in-house data to set benchmarks, action, and warning limits for these donor KPIs. Our findings whilst mining the national published data were that no cycle outcomes had been published beyond 2018, meaning these data may not be reflective of current national rates. Also, the national averages calculated will have been affected by individual clinic success rates. Knowing each clinic’s average would create a larger range, from which real world standard deviations could be determined, resulting in more meaningful warning and action limits. Such data was unavailable. The result being that, whilst UK national data is publicly available, it is flawed and insufficient for creating robust benchmarks that clinics can measure themselves against. Limitations, reasons for caution No national data, beyond 2018, is available for use in bench marking. Waiting for live birth data will delay any actions prompted by under-performance. Individual clinic success rate will have impacted the national average. Both fertile and sub-fertile populations will be included in both data sets. Wider implications of the findings The available UK data cannot be used to set robust benchmarks for donor or surrogacy KPIs. Small and new clinics are therefore unable to adequately measure their performance. With the increasing uptake of treatments involving donation and surrogacy, it is time for an international consensus on expected outcomes. Trial registration number not applicable

P-243 Effect of delayed development of embryos 7 days on embryo quality, ploidy and reproductive cycle outcomes

Abstract Study question How does delay in embryo development before Day7 affect blastocyst quality, ploidy and reproductive cycle outcomes? Summary answer Embryo quality and ploidy are statistically significantly lower in the Day7 group, no difference in implantation rate was found. What is known already In clinics that allow extended culture up to Day7, on average 5% of embryos have a 48-hour delay in development, blastulation occurs on the 7th Day (Hammond et al., 2018). Day7 blastocysts may have good morphology and be euploid, give a pregnancy and birth of a healthy baby. Back in 2013 it has been proven that embryos from patients over 35 years of age take longer to form a blastocyst (Shapiro et al., 2013). Cultivation until Day 7 is justified for couples with a poor prognosis in cycles. Study design, size, duration This was a retrospective cohort study in a private Delta Fertility Clinic of consecutive female infertility patients (n = 422) between Sept 2021 and Sept 2022. Average age of the patients was 39,7 years who underwent frozen embryo transfer (FET) of a single euploid day 5, 6 or 7 blastocyst. Then we compared the outcomes in the 5, 6 and 7 Day groups. Participants/materials, setting, methods The results of culture and subsequent biopsy of trophoectoderm with PGT-A of 2095 blastocysts (1516 were tested with PGT-A) in 482 cycles were analyzed, of these, embryos Day7 suitable for biopsy were 9.8% (149). Blastocysts were classified as good (AA/AB/BA/BB) or poor (AC/BC/CA/CB) (Gardner D.K. et al., 1999). Cultivation performed in single drops, biopsy was performed using the flicking method. Statistical analysis was performed using the Pearson’s Chi-Squared Test. Main results and the role of chance In 3.4% of cases, patients had only Day7 blastocysts. Poor quality blastocysts were predominant in D7 blastocyst group (good quality: 91.0%, 65.2%, 46.3%; poor quality: 9.0%, 34.8%, 53.7%, P < 0.001 for D5, D6 and D7 blastocysts; respectively). The number of euploid embryos was significantly lower in the Day 6 and Day 7 group compared to Day 5 (51.8% and 50.0% vs 64.4%, p < 0.001 and p < 0.001). We found no differences in cycle outcomes, implantation rate was 52,7%, 49,6% and 38,5% for 5, 6 and 7 Day respectively (P = 0,474). We speculate that this may be due to the small number of day 7 embryo transfers (n = 13), but we have 5 live births in our clinic after euploid Day7 embryo transfer. Limitations, reasons for caution Due to the decrease in the percentage of euploid embryos on day 7, such embryos should be transferred only after PGT-A. There is little information about the outcomes of Day 7 embryo transfers because they are the last embryos to be transferred. Wider implications of the findings Cultivation before day 7 should be introduced into routine practice as an option for patients over 35 years of age or with a known poor prognosis. Having previously assessed the laboratory’s capabilities and financial costs. Trial registration number not applicable

P-730 A feasibility study of the impact of the level of exposure to ambient air pollutants on outcomes of assisted reproductive technologies

Abstract Study question What is the impact of air pollution exposure on outcomes for couples having IVF treatment? Summary answer Environmental exposure to high levels of air pollutants may negatively influence IVF outcomes with potential implications for fertility treatment. What is known already Air pollutants are harmful substances in the atmosphere that have adverse effects on human health. Increased levels of air pollutants have been associated with respiratory disorders, cardiovascular disease, and increased morbidity in humans across all age groups. Existing evidence suggests that increased exposure to air pollutants may adversely affect fertility. The relationship between air pollutants and IVF outcomes remains poorly understood. Study design, size, duration This was an ethically approved prospective observational feasibility study conducted over a two-year period. Ten couples due to undergo an IVF cycle were recruited from a fertility centre in the UK. Environmental exposure to ambient air pollutant for particulate matter (PM) 2.5 and 10 micron size was measured using portable AirBeam monitors over the course of two weeks from commencement of the ovarian stimulation regime. Participants/materials, setting, methods Eligible participants were those aged 18-35 years old, undergoing fresh IVF, with a good ovarian reserve and ability to provide informed consent. Data of interest included: BMI, age, parity, ethnicity, smoking status. IVF data included: number of oocytes retrieved, embryo quality and cycle outcomes. AirBeam device data was extracted, analysed and correlated with IVF outcomes. Participants feedback was sought for qualitative input for future studies. Main results and the role of chance Total of 28,269 data points of ambient air pollutant data for PM 2.5 and 10 micron size were recorded amongst the ten participants. One participant was exposed to significantly high air pollutant levels during ovarian stimulation on certain days (PM2.5 - 81.06 µg/m³ and PM10 - 154.48 µg/m³) compared to standard annual air pollution level for the UK of 25 µg/m³ for PM2.5 and 40 µg/m³ for PM10. Two women did not have embryo transfer due to embryo arrest. Of those who had transfer, 50% (n = 4) had positive pregnancy tests however three experienced early pregnancy losses. At the time of writing there was one ongoing single viable pregnancy. On correlation of air quality data with clinical outcomes, the one participant who exhibited fluctuant very high exposure levels to the measured air pollutants, had unexpected low fertilization rate (20%) with IVF and no transfer due to embryo arrest. Of the nine participants returning the questionnaire feedback, all but one rated it acceptable to most acceptable to carry the device around. The main barrier was the size of device and battery life. All respondents were willing to recommend others to participate in a future similar study confirming feasibility to recruit. Limitations, reasons for caution As a feasibility study, with a limited sample size, our findings should be interpreted cautiously. The small cohort limits the generalisability of our results. Further research with larger sample sizes is required to validate our findings. Wider implications of the findings Understanding the impact of air pollutants on IVF outcomes is important for developing evidence-based guidance and interventions to optimise fertility treatment efficacy. Our study demonstrates the feasibility of personal air quality monitoring and emphasises the necessity for larger scale research and the practicality of pollutant exposure measurements in fertility treatments. Trial registration number REC reference: 21/NE/0233 IRAS project ID: 294240. Theramex BIRTH Grant

P-702 New era in donor programs. Is it time to leave behind the antagonist for a progestin-primed ovarian stimulation protocol? Retrospective cohort analysis of 711 cycles

Abstract Study question Are GnRH-antagonist and progestin-primed ovarian (PPOS) stimulation protocols comparable in terms of effectiveness and efficiency in an egg donor program? Summary answer The PPOS protocol would have similar efficacy to the antagonist protocol, despite a slightly lower rate of useful blastocyst, without impact on recipient’s clinical results. What is known already There are numerous studies based on the comparison of oral progestin (P) vs. subcutaneous GnRH-antagonist (A) as pituitary suppressors during ovarian stimulation with gonadotropins, showing similar results in terms of ovarian response and reproductive outcomes in IVF cycles. Limited data are available on the comparison of both protocols in egg donor programs to evaluate their effectiveness and efficiency. Study design, size, duration Retrospective and observational cohort study with 711 oocyte donor cycles included over 18 months (July 2022-Dec 2023). As pituitary suppressors during ovarian stimulation, Ganirelix was used in 394 cycles and Medroxyprogesterone in 317. We obtained 626 reception cycles (369 from A group and 257 from P group). 499 egg-recipients underwent an embryo transfer (309 form A group and 190 from P group). Live birth rates were calculated only over the 192 informative embryo transfer cycles. Participants/materials, setting, methods Variables such as duration of the ovarian stimulation, number of mature oocytes (MII), maturation rate, fertilization rate, useful blastocysts (uBL) rate and their quality (>3BB/≤3BB), clinical pregnancy and live birth rate, have been evaluated. An economic analysis has been conducted for both protocols. Statistical analysis was performed using T-Student and Chi-Square tests. Main results and the role of chance There were no significant differences between groups A and P in terms of: average stimulation days (11.44±1.45 vs. 11.39±1.38, p = 0.62), average number of MII (15.69±7.46 vs. 15.12±7.12, p = 0.30), maturation rate (78.97% vs. 80.01%, p = 0.13), and fertilization rate (68.6% vs. 70.1%, p = 0.15). However, a statistically significant difference was observed in the rate of viable blastocyst formation (uBL/2PN) between groups A and P (70.4% vs. 66.8%, p < 0.05), although there were no differences in embryo qualities obtained (>3BB: 89.4% vs. 90.6%, ≤3BB: 10.6% vs. 9.1%, p = 0.083). Regarding obstetric outcomes, no differences have been found in live birth rates between the two groups (52,4% vs 64,5%, p = 0,11). The cost of the antagonist protocol was significantly higher being 8.48% more expensive than the oral progestin protocol (p < 0.05). Limitations, reasons for caution A regulated randomization has not been used to assign donors to both treatments. The population size, although enough to provide significant differences, could be wider. The number of cycles performed with P are smaller compared to A. Most clinical pregnancy are still ongoing so these data are lacking Wider implications of the findings Besides being more donor-friendly, the progestin-primed ovarian stimulation offers a significant economic advantage. Both protocols have proven similar efficacy. Clinical data are necessary to evaluate the impact of the lower BLu rate on the reproductive outcomes. Trial registration number Not applicable

P-060 When is it the sperm’s fault? The incidence of sperm-related poor fertilization after ICSI in 13,859 matched oocyte donation cycles

Abstract Study question What is the true incidence and impact of male factor-related poor fertilization in ICSI cycles when analyzed using matched pairs of high quality donor oocytes? Summary answer In ICSI cycles with donor oocytes, male factor-related poor fertilization occurs in 3.3% of cases and contributes to 86.7% of all poor (<30%) fertilization outcomes. What is known already Opting for oocyte donation is a complex decision for couples, involving significant financial and long-term implications. This decision is typically prompted by presumed female infertility as male fertility diagnostics remain limited. Although ICSI is a highly effective treatment, cases of poor or complete fertilization failure can still occur, even when sperm parameters appear normal. This suggests the presence of unidentified male-related factors. However, the precise incidence of such factors remains poorly understood. This study aims to address this gap, offering a unique perspective, by employing a matched oocyte donation model to investigate the influence of sperm-related factors on fertilization outcomes. Study design, size, duration This retrospective cohort study analyzed 14,928 oocyte donation ICSI cycles, derived from 7,519 ovarian stimulations (OS) of 2,963 unique oocyte donors. The data were from a single center from January 2015 to December 2022. Sibling oocytes from the same OS were utilized for at least two different recipients (n = 13,859), facilitating comparisons under varying paternal conditions. Participants/materials, setting, methods Cases from the same oocyte lot with poor (<30%) and good (>65%) fertilization rates were matched to isolate sperm-related factors influencing fertilization success. Paired t-tests were used to compare outcomes. Ordinary least squares regression was used to isolate variables associated with poor fertilization, such as oocyte status (fresh versus vitrified), sperm origin (partner versus donor) and the presence of severe male factor (defined as a concentration of < 1 million/mL and/or <1% progressive motility). Main results and the role of chance The mean fertilization rate was 73.0% across all cycles analyzed. The incidence of poor fertilization (≤30%) was found to be 3.8% across the entire cohort (532 out of 13,859 cycles). Of these, 86.7% (461/532) cases using the same oocyte lot could be matched to cases with high fertilization rates (>65%) in other recipient cycles (n = 1,441), indicating that poor fertilization was male-related. We observed comparable numbers of inseminated oocytes between matched cases with high and low fertilization (7.23 ± 1.32 and 7.42 ± 1.42, respectively, p = 0.011), while the mean number of fertilized oocytes (1.44 ± 0.77 versus 6.12 ± 1.36, p = <0.001) and mean fertilization rates (20% versus 83%, p < 0.001) differed significantly. Notably, oocyte vitrification and the presence of a severe male factor negatively affected fertilization outcomes (coeff. -0.0898, p < 0.001 and coeff. -0.1500, p < 0.001, respectively). Nevertheless, the majority of poor fertilization cases (92.7%) occurred in the absence of these factors, underscoring the limitations of conventional semen diagnosis tests as predictors of poor fertilization. Across the entire cohort male factor alone accounted for 3.3% (461/13,859) of cycles with <30% fertilization rates. Furthermore, sperm-related factors were the primary cause of poor fertilization outcomes in oocyte donation cycles, accounting for 86.7% of cases. Limitations, reasons for caution Certain variables were not analyzed due to the retrospective nature and extended timeframe of the study. The matched oocyte model may overlook certain non-male factor-related instances of poor fertilization, such as procedural or technical issues. Wider implications of the findings This extensive analysis emphasizes the clinical relevance of male factor in fertilization outcomes, highlighting the need for improved semen diagnosis. It also indicates the importance of considering male-related factors in treatment decisions and shifting the focus from female-centric to more balanced fertility evaluations. Trial registration number Not applicable

P-250 Only euploidy does not ensure optimal chances for successful live birth through single blastocyst cryotransfer

Abstract Study question What does a euploid blastocyst require to provide the greatest probability of successful birth? Summary answer Morphokinetic and morphological features of the inner cell mass (ICM) and trophectoderm (TE) are crucial for optimizing live birth chances in cryo-transferred euploid blastocysts. What is known already Embryo selection through preimplantation genetic testing for aneuploidy (PGT-A) alongside frozen embryo transfer strategy enhances outcomes of single-embryo transfer cycles. While euploidy is a crucial indicator, investigations on the identification of additional criteria influencing implantation and live birth rates remain imperative. Studies suggest morphokinetic and morphological quality may supplement predictive factors for euploid embryo success, with varying correlations. The impact of factors like age or gamete origin on euploid blastocyst success remains uncertain, differentiating it from clear effects on non-diagnosed embryos. Optimizing selection criteria involves navigating the intricate interplay of these variables. Study design, size, duration This retrospective study analyses the pregnancy rate (PR) in 596 single embryo cryotransfers of full euploid blastocysts (without detected mosaicism) between February 2019 and September 2023. From these, 437 had a known outcome, and the live birth rate (LBR) was calculated. The study explored the potential impact of gamete origin, oocyte provider age, recipient age, morphokinetics, and morphological quality of ICM or TE (Gardner score) on the reproductive success of the transferred embryo. Participants/materials, setting, methods All embryos were biopsied at the blastocyst stage and successively vitrified. High-resolution next-generation sequencing was used for PGT-A. Only deferred transferences of single post-thawing intact embryos were included. Morphokinetic was assessed using the KIDscoreD5 3.1. Quantitative variables (oocyte provider age, recipient age, and morphokinetic score) were compared using the t-student test, while qualitative variables (gamete origin, morphological quality of ICM and TE) were assessed using the chi-square test. Main results and the role of chance Oocytes leading to pregnancies and live births were derived from women with ages comparable to those without success (Pregnancy: 30.0±7.1 vs. 30.8±6.8, p = 0.174; Live Birth: 30.1±7.1 vs. 30.5±6.9, p = 0.499). Similar age was also observed among recipients achieving pregnancy (41.5±5.4) and live births (41.1±5.1) compared to those who did not (Pregnancy: 41.8±5.1, p = 0.506; Live Birth: 41.5±5.3, p = 0.411). The origin of oocytes and semen (own or donor) did not significantly affect PR (Oocytes: 199/273 vs. 217/323, p = 0.130; Semen: 328/473 vs. 88/123, p = 0.224) or LBR (Oocytes: 113/205 vs. 116/232, p = 0.285; Semen: 183/347 vs. 46/90, p = 0.783). Morphokinetics played a crucial role, with euploid embryos resulting in pregnancy (7.5±1.7) and live births (7.6±1.6) exhibiting significantly higher scores than those without success (6.9±1.7; 7.1±1.7; p < 0.05).199 ICM quality did not significantly impact PR (A:211/296, B:190/275, C:15/25; p = 0.469). However, higher miscarriage rates in C-quality ICM blastocysts significantly reduced the LBR (A:116/211, B:107/205, C:6/21; p < 0.05). TE quality exhibited significant differences in PR (A:221/289, B:184/289, C:11/18; p < 0.05). Since the miscarriage rate was similar among groups (p = 0.787), LBR remained higher in A-quality TE blastocysts (A:124/209, B:98/213, C:7/17; p < 0.05). Limitations, reasons for caution As a retrospective analysis, this study is inherently limited. The influence of expansion grade on success rates remains unexplored, given the use of assisted hatching on day 3 of culture. Performing assisted hatching at the time of biopsy could potentially overcome this limitation. Wider implications of the findings The pursuit of a euploid embryo often becomes the priority in IVF laboratories. However, once the milestone is achieved, morphokinetics and embryonic morphological quality must continue to be considered. This study provides valuable insights for conveying a detailed message to patients with euploid embryos about their prospects for homebirth success. Trial registration number not applicable

P-634 Medroxyprogesterone acetate as an alternative to gonadotropin-realeasing hormone antagonist in vitrified oocyte donation cycles: embryo assessment and clinical outcome

Abstract Study question Could Medroxyprogesterone Acetate (MPA) be a good alternative to gonadotropin-realeasing hormone (GnRH) antagonist in vitrified oocyte donation cycles? Summary answer MPA is a good alternative to GnRH antagonist in vitrified oocyte donation cycles, ensuring comparable embryo quality and clinical outcome. What is known already Progestin-primed ovarian stimulation (PPOS), such as oral administration MPA in the follicular phase appears to be an effective alternative to conventional protocols, as it prevents premature LH surge and ovarian hyperstimulation syndrome. The drawback of these treatments is that it requires vitrification of oocytes or embryos because the endometrium is out of phase when embryo transfer is performed. Our previous studies have shown similar oocyte retrieval rates in fertility preservation cycles and comparable clinical outcomes in fresh donation cycles. Our objective is to expand evidence on PPOS, extending its success to new populations like vitrified donation cycles. Study design, size, duration This retrospective cohort study performed at IVI Valencia compared the effect of the MPA (10 mg/day) versus ganirelix (0.25 mg/day) on egg donors undergoing ovarian stimulation whose eggs were vitrified after retrieval. Donor cycles were divided intro groups, with 495 cycles in the MPA group and 307 in the ganirelix group. After oocyte donations and warming, the artificial intelligence based embryo assessment and clinical outcome were compared and analyzed for the two study populations Participants/materials, setting, methods 497 recipients using oocytes from the MPA group and 307 from the ganirelix group were included in the study. Post-oocyte donation and warming, a follow-up of 10,108 oocytes was performed, analyzing survival, fertilization, and blastocyst development. The embryo score obtained with the deep learning based model iDAScore v2, and the ASEBIR evaluation performed by embryologists were compared between both study populations. Finally, comprehensive clinical outcome comparisons were conducted between the two study populations. Main results and the role of chance The mean number of thawed oocytes was significantly different* between the two groups (12.80±3.54 in the MPA group vs. 12.20±3.58 in the antagonist group). Survival, fertilization, and blastocyst development rates showed no significant differences (89.83%, 76.38% and 66.22% respectively in the MPA group and 88.67%, 76.75% and 64.29% in the antagonist group). However, ASEBIR embryo assessment showed a significantly higher percentage of embryos classified as A and B in MPA group* (10.5% and 58.0% respectively vs. 7.2% and 53.6%), and more C embryos* in the antagonist group (34.3% vs. 39.2%). Artificial intelligence-based embryo assessment revealed no significant differences between the two groups*, with mean evaluations being 4.97±2.60 in the MPA group and 5.07±2.68 in the antagonist group. Regarding clinical outcomes, the MPA group had significantly higher number of frozen embryos per cycle* (4.08±2.07 in the MPA group vs. 3.65±2.00 in the antagonist group) but no disparities in implantation, clinical pregnancy, ongoing pregnancy, live birth and cumulative live birth rates. A generalized estimation equation highlighted that the study group (MPA or antagonist) did not significantly impact the live birth rate, but was significantly influenced instead by the number of thawed oocytes, recipient BMI, and transferred embryo quality assessed with iDAScore*. (*p<.05) Limitations, reasons for caution This project is limited by its retrospective and single-center nature. Despite being the largest sample size ever reported for PPOS in vitrified donation cycles, the number of patients included could be considered low. Consequently, it would be advisable to conduct a multicenter RCT to confirm the conclusions of this study. Wider implications of the findings The administration of MPA as a gonadotropin adjuvant demonstrates clinical outcomes comparable to those achieved with ganirelix in vitrified oocyte donation cycles. Its user-friendly application encourages the wider adoption of this protocols. These promising results promote the widespread use of MPA-based protocols in vitrified oocyte donation cycles. Trial registration number not applicable

P-459 Impact of a drop in serum estradiol levels after gonadotropin-releasing hormone (GnRH) antagonist on clinical outcomes of ovarian stimulation cycles in assisted reproductive technology (ART)

Abstract Study question Does a drop in serum estradiol level after the administration of a GnRH antagonist affect outcomes in ovarian stimulation cycles in ART? Summary answer A drop in serum estradiol after administration of a GnRH antagonist is related to changes in luteinizing hormone (LH) and to inferior clinical outcomes. What is known already In recent years, the GnRH antagonist protocol has become widely used to prevent a premature LH surge during ovarian stimulation in ART, with many advantages such as immediate pituitary suppression and a lower risk of ovarian hyperstimulation. However, one phenomenon intriguing professionals monitoring these cycles and reviewing blood analyses, is the decrease in serum estradiol that occasionally occurs after the administration of the antagonist. With the natural menstrual cycle in mind, this could be an undesirable effect possibly affecting clinical outcomes. Study design, size, duration This was a non-interventional, retrospective, observational cohort study. We analyzed 1678 ovarian stimulation cycles in ART in 1143 patients. Patients were treated between January 1st 2015 and November 1st 2022. Patients were 20 to 45 years old, were stimulated with human menopausal gonadotropin (hMG) or recombinant follicle stimulating hormone (follitropin α, β or δ, corifollitropin α and follitropin α + lutropin α) and a GnRH antagonist was used for pituitary suppression in a flexible protocol. Participants/materials, setting, methods Data were extracted from medical records at a tertiary infertility clinic. The difference between serum estradiol level before and after the first antagonist administration was calculated. When this value was negative, the cycle was marked as having an estradiol drop. Influence of treatment and cycle characteristics on estradiol drop, as well as influence of the drop on clinical outcomes were analyzed using generalized linear mixed effects models. Main results and the role of chance The presence of a serum estradiol drop could be calculated in 1552 cycles, of which 153 cycles (9.9%) showed a drop. There was no significant difference in the odds on cycle cancellation between cycles with and without drop (p = 0.87). Type of gonadotrophin used was significantly associated with the presence of an estradiol drop (p < 0.0001), with hMG cycles showing the lowest amount of drops (3.0%). More estradiol drops were observed with the start of antagonist administration on day six of stimulation (10.3% of cycles), compared to starting later than day six (9.1%)(p = 0.001). Serum LH at the start of the cycle was significantly higher in cycles with estradiol drop (mean±SD=4.10±4.13IU/L) than in cycles without (3.88±2.74IU/L) (p = 0.01). Decrease in serum LH levels after antagonist administration was significantly larger in cycles with estradiol drop (-5.30±7.58IU/L versus -1.66±3.13IU/L,p<0.0001). Serum LH on the day of ovulation triggering was also lower in estradiol drop cycles (1.29±1.59IU/L versus 2.24±8.13IU/L,p=0.0007). Estradiol drop was not significantly associated with the number of oocytes retrieved, 2PN fertilized, utilization rate or embryo transfer (p-values>0.05). Ongoing pregnancy and live birth were also significantly lower in cycles with an estradiol drop (13.9%) than in cycles without (25%, p = 0.01). When correcting for age, p-values remained unchanged. Limitations, reasons for caution A limitation of the retrospective study design is that stimulation protocols and any adjustments were chosen by the treating physician according to the patient’s characteristics. The authors did adjust for different cycles per patient by using generalized mixed models. Absolute numbers of estradiol drop are low, limiting optimal multivariable analysis. Wider implications of the findings Because serum estradiol drop after GnRH antagonist administration is related to changes in LH, prospective research could focus on potential optimization of the LH serum levels which could potentially ameliorate clinical outcome. Trial registration number not applicable

P-359 Ten years’ experience using cryopreserved oocytes from In Vitro Maturation (IVM) or Controlled Ovarian Hyperstimulation (COH) cycles for fertility preservation in oncologic indications

Abstract Study question Is IVM a relevant option for fertility preservation in cancer patients, considering biological/clinical outcomes post-thawing, compared to COH? Summary answer This study shows that despite a significantly altered embryo morphology within the IVM group, the clinical outcomes remain comparable to those of COH. What is known already Fertility Preservation (FP) techniques are proposed to patients with cancer to provide the possibility of childbearing using their own gametes. Currently, oocyte vitrification after COH is the standard option. IVM serves as an alternative when COH is contraindicated, urgent cancer therapy is required, or in conjunction with ovarian cortex cryopreservation. Limited live births have been reported from frozen-thawed oocytes in IVM cycles of cancer survivors. Scarce data are available for comparing biological/clinical outcomes of frozen-thawed oocytes from IVM versus COH cycles in cancer survivors. Study design, size, duration This bicentric retrospective cohort study aimed to analyze the outcomes of all oocyte warming cycles in 73 cancer survivors having undergone oocyte vitrification for FP after COH and/or IVM. All of them had oocyte retrieval before the administration of gonadotoxic treatment and returned after being cured, with their oncologist agreement, for assisted reproduction treatments, between November 2012 and January 2024. Participants/materials, setting, methods Seventy-seven warming attempts followed by ICSI respectively from 37 COH and 40 IVM cycles were analyzed. Four patients benefited from an IVM and COH cycle. Survival, fertilization, top and good-quality embryos, defined at day-2 respectively as 4 and 3-5 adequate-sized blastomeres, without multinucleation with < 20% of cytoplasmic fragments, implantation, biochemical (hCG>100 UI/mL), clinical (intrauterine sac with fetal heartbeat) and live birth rates were compared using appropriate statistical tests. Main results and the role of chance The mean age and antral follicle count at the time of FP was similar in both groups. The indications for FP were breast cancer (n = 61), hematologic malignancies (n = 7), ovarian cancer (n = 3), other (n = 2). The number of cryopreserved oocytes tended to be higher in the COH group, when compared to the IVM group (8.5±7.3 vs 5.9±4.04; p = 0.16). The mean oocyte maturation rate after IVM was 68.6±23.1%. Oocyte survival, and fertilization rates were similar in COH and IVM groups, respectively (76.4±27.0% vs 76.1±22.0%; p = 0.76) and (67.1±34.3% vs 65.3±25.4%; p = 0.36). We reported a significantly better embryo quality at day-2 in the COH group when compared to the IVM group, with respectively top-quality embryos (44.0±34.2% vs 26.1±33.4%, p = 0,04) and good-quality embryos (62.2±38.0% vs 42.8±40.8%, p = 0.049), and also a significantly higher number of useful embryo in the COH group (2.7±2.6 vs 1.5±1.2, p = 0.03). Regarding clinical outcomes, the results were similar in COH and IVM groups, in terms of implantation rates (12.2±30.4% vs 15.5±35.6%; p = 0.86), biochemical (32.3% (10/31) vs 17.9% (6/28); p = 0.39), clinical pregnancies (25.8% (8/31) vs 17.9% (4/28); p = 0.54), live birth rates ( 25.8% (8/31) vs 14.3% (4/28); p = 0.34). Limitations, reasons for caution Statistical power to compare IVF outcomes after COH and IVM is limited by the few women who returned to use their frozen oocytes. The subjective nature of embryo morphology assessment. Wider implications of the findings This study is the largest evaluating frozen-warmed oocytes from IVM cycles in cancer patients, with 5 live births newly reported. A higher oocyte-yield may be necessary in IVM as the number of useful embryos is significantly lower. Novel approaches are being developed to improve maturation rates following IVM. Trial registration number Not applicable