Frozen Embryo Transfer Research Articles

P-452 A decrease in serum progesterone-levels (P4) during early luteal phase in modified-natural frozen embryo transfer (mNC-FET) is significantly associated with lower pregnancy rates

Abstract Study question Does a serum progesterone-level (P4) increase (+ΔP4) or decrease (-ΔP4) through luteal phase (LP) compromise ongoing pregnancy rate (OPR) or miscarriage rate (MR) in mNC-FET? Summary answer A P4 decrease (-ΔP4) through luteal phase in mNC-FET is significantly associated with lower OPR and higher MR compared to P4 increase (+ΔP4) What is known already Increasing evidence has been recently reported in literature according to the relevance of P4 round FET but also on b-HCG day in artificial and natural FET (AC-FET; NC-FET). Otherwise, mNC-FET gives the chance for triggering and scheduling FET, with less days of monitoring for patients, but keeping the advantages described according to lower risk of preeclampsia through the relaxin production by the corpus luteum. Nevertheless, no studies have been reported according to reproductive outcomes and P4 increase or decrease through the luteal-phase in mNC-FET, as it has been done in fresh embryo transfer (IVF-transfer) Study design, size, duration This is a retrospective observational study led at a single university-affiliated fertility center. Overall, 504 women undergoing mNC-FET between October 2019-October 2023 were included for the analysis. Among them 373 (74%) were homologous-FET cycles (hom-FET), 123 (24%) heterologous-FET cycles (oocyte donation) (het-FET) and 8 (1.6%) embryo donation-FET cycles (don-FET) Participants/materials, setting, methods mNC-FETs were performed seven days after HCG-trigger (HCG+7) and on the sixth day of vaginal progesterone treatment. P4-levels were measured on the day before FET (D5-P4) and on β-HCG day (β-P4). Pregnancy outcomes were analysed according to + ΔP4 or -ΔP4 between those two time intervals through the LP in mNC-FET. Progesterone treatment continued until the 10th week of pregnancy.Chi-squared test was used to compare proportions and ROC-curve analysis to identify the best cutoffs for outcomes Main results and the role of chance Patients’ age at oocyte retrieval was 33.5 and 38.4 at FET. No differences were described according to epidemiological features. Mean β-P4 and D5-P4 (ng/mL) were 25.15 ± 12.8 and 24.88 ± 6.9 respectively. ΔP4 was reported as positive (+ΔP4) in 52.2% (n = 263), and negative (-ΔP4) in 47.8% patients (n = 241). Mean ΔP4 was +0.26 ± 13 ng/mL. Overall reproductive outcomes were: OPR 47.8% and miscarriage rate (MR) 12.3%. OPR was significantly lower (15.8% vs 77.2%, p = 0.00) and MR significantly higher (19.1% vs 11%, p = 0.099) in case of -ΔP4 compared to + ΔP4. Predicting factors for OPR were b-HCG (ROC-AUC (95% CI) 0.920 (0.896-0.945)), β-P4 (ROC-AUC (95% CI) 0.860 (0.827-0.893)) and ΔP4 (ROC-AUC (95% CI) 0.859 (0.826-0.893)). The optimal cut-off value for OPR were β-HCG > 45.15 UI, β-P4 >22.6 ng/mL and ΔP4 > 0.73 ng/mL, with a sensitivity and a specificity of 0.84-0.75, 0.97-0.78 and 0.83-0.78 respectively. OPR in patients with β-HCG > 45.15 UI and β-P4 >22.6 ng/mL was significantly higher (81.7%) compared to patients with β-HCG > 45.15 UI or β-P4 > 22.6 ng/mL (53%), and patients with β-HCG ≤ 45.15 UI and β-P4 ≤ 22.6 ng/mL (2.6%) (p < 0.001) Limitations, reasons for caution The main limitation of this study is its retrospective nature and that conclusions cannot be extrapolated to other methods for endometrial preparation for FET, although conflicting pregnancy outcomes according P4-levels have also been described in either natural or artificial FET. No live birth rate was available at the period study Wider implications of the findings ΔP4 through LP seems to be relevant for pregnancy outcomes in mNC-FET as -ΔP4 significantly reduces OPR and increases MR compared to + ΔP4. Evaluation of ΔP4 between the day before FET (D5-P4) and on β-HCG day (β-P4) may be a useful biomarker to predict ongoing pregnancy rates in mNC-FET cycles Trial registration number Not applicable

O-152 Pre-implantation genetic testing for aneuploidies (PGT-A) improves reproductive outcomes in advanced maternal age patients undergoing IVF/ICSI: a multicentre retrospective cohort study with propensity score matching

Abstract Study question In patients > 37 years undergoing IVF/ICSI, does PGT-A improve live birth rates (LBR) and cumulative live birth rates (CLBR)? Summary answer In advanced maternal age women with ≥1 embryo to transfer, PGT-A improves the live birth and cumulative live birth rates. What is known already The age-related rate of aneuploidy remains a major cause of IVF failure. Therefore, PGT-A has been proposed as a method to select embryos with the highest implantation potential. Previous studies have shown that women younger than 37 years old do not benefit from PGT-A given the comparable outcomes in terms of implantation, clinical pregnancy, and live-birth rates. Moreover, PGT-A may also be inherently ineffective given the risk of mitotic mosaicism, sampling errors and misinterpretation of results. However, we are currently lacking solid scientific evidence to support whether this approach benefits advanced maternal age women. Study design, size, duration A multicenter retrospective cohort study was conducted including 9328 patients >37y undergoing their first IVF/ICSI cycle with an oocyte retrieval performed between 1/01/2013-31/07/2021 in a multinational private fertility clinic. The study group (n = 4664) included patients who performed PGT-A. The control group included patients without PGT-A (n = 4664) and was selected by propensity score matching adjusted for age at oocyte retrieval, number of oocytes retrieved and year of oocyte retrieval. Participants/materials, setting, methods The primary outcome was CLBR (delivery of at least one live birth per started cycle, including the fresh and subsequent frozen embryo transfer cycles). The secondary outcomes were LBR and time to pregnancy. The analysis was conducted including all patients with an initiated cycle of ovarian stimulation and also per embryo transfer. Comparisons are presented as adjusted odd-ratios (adjOR) and 95% confidence intervals (95%CI) following multivariable logistic regression (LBR) or cox regression (CLBR) analysis. Main results and the role of chance Patients in the PGT-A group had more oocytes retrieved (11.03±6.82 vs 9.24±6.15, p < 0.001), and a higher number of available blastocysts (2.82±2.21 vs 1.22±2.00, p < 0.001). In the PGT-A group, 13.153 embryos were analysed, with an euploidy rate of 29.30% (n = 3854). In total, 49.83% (n = 2324) patients did not undergo embryo transfer due to unavailable euploid embryos. Considering all patients that initiated ovarian stimulation, the PGT-A group presented a higher unadjusted CLBR per started cycle (27.38% vs 21.81%, p < 0.001). Considering only patients who underwent embryo transfer, a total of 5934 embryo transfers were analysed (n = 3166 in the control group and n = 2768 in the PGT-A group). Following multivariable logistic regression analysis, LBR and CLBR were significantly higher in the PGT-A group (respectively, adjOR 1.56 [95% CI 1.38-1.77], adjOR 1.53 [95% CI 1.39-1.68]). Following the transfer of 5 embryos, the CLBR was approximately 100% in the PGT-A group and 74.51% in the control group. Survival analysis was also perfomed to assess the impact of PGT-A on time to pregnancy. Despite the fact that from 6 months onwards the CLBR was higher in the PGT-A group, the median time to pregnancy was higher in the PGT-A group (3.27 (95%CI 3.16-3.40) vs 2.74 months (95%CI 2.57-3.03). Limitations, reasons for caution This study is limited by its retrospective design and low number of women with more than 3 embryos transferred. Also, the fact that only the first IVF/ICSI cycle was analysed provides a proper patient counselling in this specific context but does not provide data on repeated cycle outcomes. Wider implications of the findings Our findings suggest that, in women older than 37 years with at least one available embryo to biopsy, performing PGT-A may improve the reproductive outcomes in terms of LBR and CLBR, providing a useful clinical tool for embryo selection. Trial registration number not applicable

O-025 An artificial intelligence (AI) model non-invasively evaluates endometrial receptivity from ultrasound images, surpassing endometrial thickness (EMT) in predicting implantation

Abstract Study question Can an AI image-based model be trained to predict whether an endometrium, prior to progesterone, is receptive for successful embryo implantation from ultrasound images? Summary answer An endometrial receptivity AI model, utilizing ultrasound images and clinical features, is predictive of successful implantation and outperforms endometrial thickness as a predictor of implantation. What is known already Despite its importance in successful embryo implantation and subsequent live birth, endometrial receptivity is difficult to measure. The standard of care at some clinics is to cancel an embryo transfer if EMT is measuring less than 7 mm on ultrasound assessment – however, achieving an EMT threshold does not guarantee success, even with euploid blastocysts. Currently available receptivity tests (e.g. endometrial receptivity assays) are unreliable and have not shown significant improvements in reproductive outcomes, necessitating the development of new evaluation methods for endometrial receptivity. AI can potentially address this gap in clinical care and understanding, aiming to increase patient success. Study design, size, duration 79,602 ultrasound images (40,910 patients) of the endometrium, on the day of progesterone start according to patient’s frozen embryo transfer cycle, were retrospectively collected from 4 clinic networks including 70 clinic locations. PGT-A outcomes and blastocyst quality were available for 15,466 and 36,070 blastocysts respectively, with 14,538 having labels for both. Different image samples (based on embryo quality) were selected to train and test several AI models, with implantation (positive beta-hCG) as a binary outcome. Participants/materials, setting, methods Three criteria for negative (implantation) class sample selection were tested for receptivity model development: 1) high- or medium-quality and/or euploid blastocysts; 2) high-quality blastocysts; 3) all blastocysts. Models were ensembles consisting of an image-based deep learning (DL)-model and a feature-based machine learning (ML)-model. Model performance was measured by Area-under-the-curve (AUC), sensitivity, and specificity. Feature importance from the ML model was assessed, while receptivity model performance was compared to the power of EMT to predict implantation. Main results and the role of chance A receptivity model trained on scenario 1) (n = 27,424) achieved AUC 0.613, sensitivity 0.716, and specificity 0.439 on a test set of 9197 samples, in predicting implantation. Another receptivity model trained on scenario 2) (n = 25,625) achieved AUC 0.627, sensitivity 0.637, and specificity 0.543 on a test set of 8642. Whereas a third receptivity model trained on scenario 3) (n = 31,238) was selected for further analysis as it attained the best performance with AUC 0.631, sensitivity 0.628, and specificity 0.556 on a test set of 10,422. The ensemble model also utilizes relevant clinical features, which were ranked by importance to model predictions: EMT; progesterone blood test value; age at transfer; previous total embryo transfers; days between ultrasound date and transfer date; age at retrieval; and oocyte origin. EMT was assessed for its ability to predict implantation at thresholds between 5–20 mm. The threshold that best separates positive and negative implantation was determined by evaluating AUC on a validation set of 5682. A threshold of 8.8 mm achieved an AUC 0.576, sensitivity 0.694, and specificity 0.455 in predicting implantation on a test set of 5686. However, the receptivity model AUC (0.631) was significantly higher (p < 0.001; DeLong test for differences in AUC), outperforming EMT predictability. Limitations, reasons for caution The endometrial receptivity model was built and tested on retrospective frozen embryo transfer data. Results should be corroborated in prospective and non-selection studies, as well as in multiple geographical locations (all clinics included reside in the United States). The dataset requires greater diversification, with a greater representation of EMT (<7mm). Wider implications of the findings This study indicates that an AI model can be built to predict implantation from ultrasound images and clinical features, surpassing current standards - EMT alone. Further experimentation, with additional clinical features, may improve performance to facilitate development of a model that can accurately predict the gold-standard of live birth. Trial registration number Not applicable

P-407 Exploring the effectiveness of tailoring estradiol supplementation duration to mimic the natural cycle length in artificial endometrial preparation for frozen embryo transfer cycles

Abstract Study question Is an estrogen supplementation duration similar in length to the follicular phase of a natural cycle associated with a better clinical pregnancy rate? Summary answer An estradiol supplementation duration, which is proportional to the natural follicular phase length, results in significantly better outcomes compared to shorter exposure durations What is known already The last decade witnessed a major increase in the use of single euploid frozen embryos. Artificial endometrial preparation (AEP) has proven to be effective to prepare the endometrium for implantation. However, several features of AEP need to be clarified mainly the duration of estrogen supplementation and until now no study took into consideration the difference between exogenous estrogen supplementation and the actual length of the follicular phase of each patient during AEP. Furthermore, most of the studies focused on upper limit of estrogen exposure while few considered the lower limit. Unfortunately, the results on pregnancy rates were mixed. Study design, size, duration 663 single euploid frozen embryo transfer cycles were included. Patients underwent vaginal ultrasound and hormonal blood measurement (Estradiol, Progesterone) on day 2 of their cycle. Estradiol valerate (4 mg the first 2 days then 6 mg daily, Orally) was started on the same day and another control was done around day 10. When triple lining pattern of the endometrium was seen, vaginal progesterone was initiated (800 mg daily) and SET was done after 120 hours. Participants/materials, setting, methods Patients with reported regular menstrual cycle (25-35 days) were included and the difference between estrogen supplementation and the actual follicular phase was calculated for each patient. Patients were sorted into 2 groups as follows: 231 women with normal interval (±2 days of follicular phase length), and 432 women with short interval (-3 days or shorter). Only the first single euploid embryo transfer cycles were analyzed for these patients. Main results and the role of chance Whereas patients had similar characteristics in both groups, the corresponding clinical pregnancy rates in normal and short supplementation groups were 69.3% (160/231) and 64% (277/432), respectively. After balancing the groups for BMI, embryo quality and endometrial thickness with inverse treatment probability weighting, those who received estradiol supplementation proportional to their natural follicular phase length had significantly higher clinical pregnancy rates compared to those who received it for shorter durations (adjusted OR: 1.48, 95% CI: 1.16 – 1.89, P = 0.002). Serum estradiol levels were available for 523 cycles, the clinical pregnancy rate in those within the 1st quartile (<155pmol/L), 2nd to 3rd quartile (155 to 275pmol/L) and 4th quartile (>275pmol/L) were 70%, 64.7% and 63%. After adjusting for BMI and embryo quality, higher (>275pmol/L) (adjusted OR: 0.84, 95% CI: 0.53-1.32, P = 0.442) and lower(<155pmol/L) (adjusted OR: 1.37, 95% CI: 0.85-2.22, P = 0.202) estradiol levels were not significantly associated with clinical pregnancy. Limitations, reasons for caution The present study could not address the influence of very long estrogen supplementation on clinical pregnancy rate due to limited samples. Further prospective studies, including larger populations, are needed to confirm our findings Wider implications of the findings Our data indicate that mimicking individually the natural cycle regarding estrogen supplementation duration in AEP for single euploid embryo transfer cycles can produce significant improvement in clinical pregnancy rates. Trial registration number not applicable

O-147 Role of serum progesterone levels and subcutaneous progesterone supplementation in endometriosis patients undergoing artificial cycle frozen embryo transfer

Abstract Study question Is there any impact of serum progesterone levels and subcutaneous progesterone supplementation on live birth rate in endometriosis patients undergoing Artificial Cycle-Frozen Embryo Transfer (AC-FET)? Summary answer Endometriosis patients have comparable progesterone levels before transfer to those without endometriosis. Progesterone supplementation results in similar live birth rate (LBR) to the general population. What is known already Progesterone (P4) resistance is a hallmark of uterine alterations in endometriosis. This disease could disrupt balance between progesterone and estrogen signaling pathways, resulting in estrogen dominance and progesterone resistance at the receptor level, which warrants a deeper exploration for adjusting dosages when performing AC-FET. A recent retrospective study highlights the potential significance of a progesterone threshold when using vaginal and intramuscular progesterone systematically in AC-FET, correlating with a significantly higher LBR for endometriosis-patients. However, no current studies have compared LBR according to P4 the day before blastocyst-transfer and progesterone supplementation in endometriosis versus non-endometriosis-patients undergoing AC-FET with standard vaginal treatment. Study design, size, duration This is a retrospective cohort study including 985 cycles undergoing autologous AC-FET with standard vaginal progesterone treatment (600 mg/day) at a university-affiliated fertility center from January 2019 to December 2022. 168 cycles were from patients with confirmed endometriosis. LBR was evaluated in both groups based on P4 levels the day before transfer. Progesterone supplementation via SC injection (25 mg/day) was administered when levels were deemed low (<10.6 ng/mL based on our previously published research). Participants/materials, setting, methods Endometrial preparation involved oral estrogens at 6 mg daily from the begging of menstrual cycle. Micronized vaginal progesterone (600 mg/day) was added when thickness reached 7 mm. P4 was measured before embryo transfer; supplementation (25 mg SC injection) was added if < 10.6 ng/mL. FET occurred 6 days after initiating luteal phase support. Treatment continued until the pregnancy test. If pregnant, treatment ceased at 10 weeks of amenorrhea. Main results and the role of chance Comparisons between endometriosis and non-endometriosis groups revealed similar baseline characteristics regarding age, BMI, parity, number of embryos transferred, and embryo quality. The number of cycles with levels ≥10.6 ng/mL before transfer were comparable between patients with and without endometriosis (aOR 0.98, 95% CI 0.65-1.47) according to a multivariable logistic regression analysis adjusting for age, BMI, and prior progesterone levels <10.6ng/mL the day before transfer. Unadjusted findings demonstrated equivalent clinical pregnancy, miscarriage, and live birth rates in endometriosis compared to non-endometriosis patients. A subsequent multivariable logistic regression analysis to analyze LBR was conducted, considering four groups: Group 1: Endometriosis with progesterone <10.6ng/mL and SC supplementation (51 patients) Group 2: Endometriosis with progesterone ≥10.6ng/mL (117 patients) Group 3: Non-endometriosis with progesterone <10.6ng/mL and SC supplementation (274 patients) Group 4: Non-endometriosis with progesterone ≥10.6ng/mL (543 patients) Adjusted for age, BMI, and embryo quality, Group 1 was considered as the reference. Results showed comparable live birth rates between the reference group and Group 2 (aOR 0.79, 95% CI 0.36-1.74), Group 3 (aOR 0.91, 95% CI 0.45-1.8), and Group 4 (aOR 1.9, 95% CI 0.71-2.74). Subcutaneous supplementation for endometriosis patients with P4<10.6ng/mL the day before embryo transfer led to similar LBR compared to the other groups. Limitations, reasons for caution The main limitation of this study is the single-center retrospective approach. While the total number of endometriosis patients is 168, the representation of endometriosis patients in group 1 may be a study limitation. Furthermore, all endometriosis stages were analyzed together although this may be clinically distinct entities. Wider implications of the findings Endometriosis patients have the same risk to have P4<10.6ng/mL the day before FET as non-endometriosis patients. Vaginal progesterone, with subcutaneous supplementation if necessary, appears user-friendly, leading to a comparable live birth rate to that of patients with normal progesterone levels before transfer, regardless of endometriosis status. Trial registration number not applicable

P-588 Serum Luteinizing Hormone levels before progesterone supplementation are significantly associated with live birth rate in single euploid frozen embryo transfers performed in hormonal replacement cycles

Abstract Study question Do luteinizing hormone (LH) levels measured prior to initiating progesterone supplementation influence live birth rate (LBR) in artificial frozen-thawed single euploid blastocyst transfer cycles? Summary answer Serum LH levels, measured prior to progesterone initiation in artificial frozen-thawed single euploid blastocyst transfer cycles, are significantly associated with LBR. What is known already In the absence of a dominant follicle, estrogen supplementation in artificial endometrial preparation for frozen embryo transfer (FRET) can lead to a rise in endogenous LH levels, as observed in a natural cycle. Since the LH rise is a key feature in natural conception and the embryo, the endometrium, and the myometrium display receptors for LH, the rise observed during FRET preparation may have an impact on the clinical outcomes of the treatment. Previous studies found contradictory results hence none of them excluded embryo aneuploidy by implementation of preimplantation genetic testing for aneuploidies and the transfer of euploid embryos. Study design, size, duration Retrospective analysis of 639 frozen-thawed single euploid blastocyst transfer cycles performed in a tertiary referral IVF center from January 2018 to August 2023. Cycles with hormonal pre-treatment or pituitary suppression were excluded. Participants/materials, setting, methods Single euploid FRET cycles were included. Oral estradiol administration commenced on cycle-day 2/3. Estradiol, progesterone, and LH were measured at the start of endometrial preparation and up to 3 days before progesterone initiation, and the slope of LH was calculated. Patients were stratified in groups according to their LH values before progesterone administration, and the impact of LH on LBR and implantation rate was assessed. Logistic regression analysis was performed to adjust for potential confounders. Main results and the role of chance In total 639 cycles were included. Patients’ characteristics (mean+/-SD) were: age 33.2±5.9 years; BMI 27.5±4.9 kg/m2. The median duration of estrogen administration was 15 days (range: 11-27 days). The overall implantation rate and LBR were 65.9% (421/639) and 46.9% (300/639), respectively. Patients were stratified into six groups according to their LH levels prior to progesterone supplementation: <10th percentile (≤6mIU/ml, n = 57), p10th-p25th (>6 to ≤ 8.5mIU/ml, n = 81), p25th-p50th (>8.5 to ≤ 12.4mIU/ml, n = 176), p50th-p75th (>12.4 to ≤ 18.1mIU/ml, n = 180), p75th-p90th (>18.1 to ≤ 25.0mIU/ml, n = 91) and >p90th (>25.0mIU/ml, n = 54). A significant trend for higher LBR with increasing serum LH levels was observed (Cochran-Armitage Test, P = 0.041) but not for implantation rate (P = 0.158). Those with higher basal serum estradiol levels before estrogen supplementation had a steeper LH increase from basal to progesterone-supplementation day (0.40 mIU/mL higher per 10pmol/L increase in basal estradiol, P = 0.027). Regression analysis identified as independent predictors of LBR BMI (OR 0.96, 95%CI: 0.93-0.99) and embryo quality (CC vs. AA p < 0.001, CB vs. AA p = 0.027, BC vs. AA p = 0.013). Patients with steeper LH increases from estrogen to progesterone-supplementation day had higher LBR in both univariable (OR:1.27, 95%CI: 1.00–1.63, P = 0.052) and multivariable analyses (OR:1.26, 95%CI: 0.97–1.64, P = 0.085) but the difference didn’t reach statistical significance. Limitations, reasons for caution The retrospective design of the study is a limitation. Results should be interpreted with caution due to the small number of patients in the lowest and highest LH percentile groups. Wider implications of the findings The results of this study suggest that serum LH levels measured before progesterone supplementation may have an impact on the clinical outcome of artificial frozen-thawed blastocyst transfer cycles. Further studies with a higher sample size are necessary to confirm or refute our findings. Trial registration number not applicable

P-686 Optimal follicle size for triggering modified natural frozen embryo transfers

Abstract Study question What is the optimal follicle size threshold for performing trigger in modified natural cycle frozen embryo transfers (mNC-FET) cycles Summary answer The optimal follicle size threshold for performing trigger is 16 or 17, depending on the clinic’s preference to risk too early or too late triggering What is known already Recent studies reported higher fetal and maternal obstetrical complication rates are observed in artificial cycles compared to natural cycle frozen embryo transfers (NC-FET), making the natural cycle (NC) the preferred method. The modified natural cycle (mNC) provides a partial solution to overcome the disadvantages of the NC, mostly its repeated visits and inability to conveniently schedule the transfer. In a recently published large RCT, pregnancy rates between NC and mNC were similar, but many patients allocated to the mNC group had an LH surge prior to the hCG injection. Study design, size, duration A retrospective study consisting of 5,862 NC-FET was performed between 2018 and 2023 in a large tertiary hospital. Participants/materials, setting, methods Statistical analysis was conducted to determine the optimal follicle size threshold for triggering, for each threshold between 12-20, under the following assumptions: Clinic is closed on Sundays, ultrasound is initially performed on day 8 of the cycle and every 2 days afterwards, trigger is performed if the follicle size is at or above the threshold, unless clinic is closed 2 days after the current test day in which case no trigger was given. Main results and the role of chance The analysis measured 2 main outcomes for each trigger size threshold: The probability of triggering too early, defined as shifting the ovulation by 3 or more days. The probability of spontaneous LH surge to occur before triggering, possibly leading to transfer cancelation due to clinic closure on the designated transfer day. The traditional follicle size-based algorithm performed as follows: [Follicle size threshold]: ] Early trigger probability], [Closed day transfer probability] 12: 71.9%, 0.1% 13: 61.7%, 0.1% 14: 49.0%, 0.2% 15: 33.9%, 0.6% 16: 21.3%, 1.3% 17: 12.9%, 2.8% 18: 7.3%, 4.5% 19: 3.4%, 6.7% 20: 2.2%, 8.6% As can be seen from the results the optimal trigger threshold is either 16 or 17, depending on whether reducing transfers on days the clinic is closed has a higher importance than preventing a very early trigger day. Limitations, reasons for caution This was a retrospective study that performed statistical analysis to determine the probability of achieving each result based on the described logic. A prospective randomized clinical trial is warranted to validate the algorithm’s performance and consider variables that could not be accounted for, such as the patient’s endometrial width. Wider implications of the findings NC-FET protocols require the ability to adapt the transfer to clinics’ requirements. Given a traditional threshold-based methodology for triggering, a threshold of 16-17 is optimal depending on the risk preference of a clinic. Utilizing more advanced artificial intelligence algorithms based on ovulation prediction can significantly reduce both risk types. Trial registration number Not applicable

P-585 Vaginal progesterone associated with oral dydrogesterone versus vaginal progesterone for luteal support in letrozole-hcg cycles for thawed embryo transfer: a non-inferiority prospective cohort study

Abstract Study question Does micronized vaginal progesterone (MVP) associated with oral dydrogesterone (DYG) an alternative for luteal support in Letrozole-hcg cycles for thawed embryo transfer? Summary answer The association of MVP and DYG is a non-inferior alternative to only MVP for luteal support in thawed embryo transfer in Letrozole-hcg cycles. What is known already Endometrial preparation is essential for thawed embryo transfer. Several protocols involving different luteal support with progesterones are available. Moreover, the presence of corpus luteum decreases the obstetrical morbidity mainly linked to hypertensive disorders. Letrozole-hcg administration is a good alternative for frozen embryo transfer (FET). However, the literature lacks information about the comparison among the different protocols for luteal support in Letrozole-hcg cycles. Dydrogesterone is an oral progesterone with some unique characteristics which could be utilized with some advantage for luteal support, including oral administration and some immunological activity. Study design, size, duration This is a prospective non-inferiority cohort study performed at an infertility clinic including patients performing the first FET cycle during 2023. Reproductive outcomes were compared between patients receiving 600 mg (3x200 mg) of MPV or 40 mg of DYG plus 400 mg of MVP after Letrozole-hcg administration. Participants/materials, setting, methods All patients (aged 23-39 years) undergoing their first FET cycle during 2023 were included in this study (n = 169), divided into two groups: MVP+DYG (n = 54) or MVP (n = 115) for luteal support after Letrozole-hcg. Letrozole was administered for 5 days (2,5 mg/bid) and hcg was done when a dominant follicle reached 18 mm with a follicular endometrium measuring at least 7 mm. Main results and the role of chance Both groups were equivalent in terms of age, infertility aetiology, BMI and AMH (P > 0.05). Moreover, the proportion of cleavage or blastocyst stage was also similar between both groups (57% blastocyst transfer for MVP+DYG and 50% blastocyst transfer for MVP group, P > 0.05). The number of transferred embryos was (mean ±SD) 1.6±0.5 for both groups, P > 0.05. Furthermore, the number of top-quality embryos (cleavage stage or blastocyst) was also similar, P > 0.05. Moreover, clinical pregnancy (> 12 weeks) was 42% in MVP+DYG group versus 31% in the MVP group (-0.22-1.27, P = 0.156) and the early pregnancy loss per positive hcg test did not differ (18% for MVP+DGY and 22% for MVP, P = 0.687). In addition, we performed a multivariable analysis controlling possible confounders for clinical pregnancy: BMI, age, AMH, embryo quality, infertility aetiology and embryo stage during the transfer, and only age (0.86; 95%CI -0.229 to -0.064, P = 0.001) was related to clinical pregnancy. Limitations, reasons for caution The main limitation is the cohort design of our study, with an inherent risk of bias (selection bias). Moreover, we calculated this study to achieve the power for a non-inferiority comparison, not superiority comparison. Wider implications of the findings This is the first study comparing MVP+DYG to only MVP in patients submitted to FET using the Letrozole-hcg protocol. We demonstrated in this non-inferiority study the usefulness of adding DYG. Moreover, our results were promising showing a trend towards better pregnancy rates after MVP+DYG. Trial registration number not applicable

P-614 The use of home ovulation prediction kits (OPKs) in true natural cycle frozen embryo transfer (NC FET)

Abstract Study question Do urinary OPKs have inferior ability to detect the LH surge compared to daily serum monitoring among patients undergoing true NC FET? Summary answer OPKs are highly accurate and may serve as reliable tests to detect the LH surge among patients undergoing NC FET. What is known already Frozen embryo transfers continue to increase worldwide and recent evidence suggests natural cycle protocols may be superior to hormone replacement protocols because of lower risk of miscarriage and lower risk of pregnancy complications. Patients undergoing NC FET attend multiple clinic appointments which has been associated with increased patient stress levels during fertility treatment. OPKs have been found to be accurate at detecting the LH surge in the trying to conceive population and have high user acceptability. Study design, size, duration A prospective single cohort study including 139 fertility seeking participants was completed at an academic-affiliated fertility center for a duration of 12 months. Participants/materials, setting, methods Patients scheduled for NC FET (regular cycles 27-35 days, mid luteal progesterone >30 nmol/L, no luteal phase concern) with the ability to provide informed consent and access to SMS texting devices were eligible for participation. On the same day they started daily morning bloodwork as per the standard protocol (2-3 days prior to anticipated LH surge), participants began twice daily OPK testing. Upon exiting the study, patients completed a questionnaire on satisfaction with OPK use. Main results and the role of chance LH surge detection rate was 85.6% (n = 119/139) with serum monitoring and 93.5% (130/139) with OPK use (Kappa agreement 90.7%, K = 0.51, p < 0.001). Among patients with a serum-detected LH surge, OPK was positive within +/- 12 hours of the serum LH surge detection in 84.8% of patients. In 23.7% of cycles, OPK was positive the same morning as serum blood work. In 27.1% of cycles, OPK was positive 12h prior and in 33.9% of cycles, OPK was positive 12h after serum LH surge detection. Actual NC FET cycle cancellation rate was 16.6% (n = 23/139) compared to an anticipated cycle cancellation rate of 20.9% (29/139) if OPKs had been used to initiate serum monitoring. The average reduction in the number of serum monitoring visits and distance travelled in kilometers with OPK use was 3.9 visits (SD 2.1) and 155km (SD 174), respectively. The majority of participants reported satisfaction with OPK use. Of 135 patients, 110 (81.5%) strongly agreed the OPK was easy to use, 100 (74.1%) strongly agreed they would be open to using OPKs in future fertility treatments and 120 (88.9%) reported a reduction or no impact on stress levels associated with fertility treatments. Limitations, reasons for caution This study only used Clearblue Digital Ovulation Tests and the reported reliability in our study cannot be extrapolated to all OPKs. Additionally, the accuracy of the reported serum LH surge detection rate may be limited by physician specific definitions of serum LH surge. Wider implications of the findings OPKs are highly accurate and may serve as a reliable trigger for serum monitoring in NC FET. While their use would reduce the number of clinic appointments and distance travelled for patients undergoing NC FET cycles, patients should be advised OPK use may be associated with higher cycle cancellation rates. Trial registration number Not applicable

P-742 In-vitro fertilization outcomes after laparoscopic repair of cesarean scar defect

Abstract Study question Does laparoscopic repair of cesarean scar defect improve in-vitro fertilization (IVF) outcomes? Summary answer Laparoscopic (LSC) repair of cesarean scar defect (CSD) should selectively indicated to patients experiencing repetitive pregnancy failure or having an increased depth of niche What is known already Cesarean section (CS) rate has markedly from 7% in 1990 to an estimated 29% of all births by 2030. CSD, also known as isthmocele or uterine niche, has emerged as a cause of secondary infertility, frequently encountered with recurrent implantation failures and cycle cancellations because of the endometrial fluid collection both in endometrium and uterine lower segment of cesarean scar. Study design, size, duration This is a retrospective study encompassing total of 62 patients. With 50 patients undergoing expectant management, 12 undergoing LSC repair of CSD at a single IVF center from 2019 to 2023. Primary outcomes included the clinical pregnancy rate and time to pregnancy, while secondary outcomes were the depth of CSD and residual myometrial thickness. Of the 72 patients, 68 patients underwent frozen embryo transfer. Participants/materials, setting, methods Patients with secondary infertility who had experienced more than two instances of implantation failure or cycle cancellation due to endometrial fluid collection were included. Laparoscopic repair of CSD was performed by a single gynecologic oncologist in accordance with the physician’s preference and patient consent. For patients in expectant management, diagnostic hysteroscopy and endometrial fluid suction were conducted prior to embryo transfer. Main results and the role of chance The age, BMI, gravidity, parity, or the number of previous cesarean section showed no statistical differences between the expectant management and the LSC repair group. The uterine position, either anteflexion was similar across groups. (all p value >0.05). Both the clinical pregnancy rate and live birth rate did not significantly differ between the expectant management group and the LSC repair group (26.0% vs 50.0%, p = 0.149, and 32.0% vs 60.0%, p = 0.149, respectively). The mean time to pregnancy was 7.38 months in the expectant management group and 9.80 months in LSC repair group, showed no significant difference (p = 0.240). Correlation analysis revealed a significantly moderate correlation between the initial depth of CSD and the depth of CSD at embryo transfer with clinical pregnancy (r = -0.424, P = 0.001). Furthermore, our data indicated that the CSD depth at embryo transfer was significantly impacted on clinical pregnancy outcomes from the multivariate regression logistic analysis (OR = 0.522, 95% CI [0.332 – 0.823]). Limitations, reasons for caution This study is retrospectively designed and including small sample size, caution is required in interpreting the findings. Wider implications of the findings This study suggests that the depth of niche influences clinical pregnancy outcomes. Laparoscopic repair may offer a viable treatment option who have experienced multiple failed cycles and increased depth of niche. Future studies with larger population studies may further indicate the LSC repair based on the depth of CSD. Trial registration number not applicable

P-650 Cumulative live birth rate after use of capacitation in vitro maturation in women with predicted excessive response to ovarian stimulation: an analysis of 1,563 cycles

Abstract Study question What is the cumulative live birth rate in biphasic (capacitation) in vitro maturation (CAPA-IVM) cycles in women with predicted excessive response? Summary answer The cumulative live birth rate achieved after CAPA-IVM in women with predicted excessive response was 37.8%. What is known already In vitro maturation (IVM) is an alternative infertility treatment for women at high risk of complications during conventional in vitro fertilisation with ovarian stimulation. There is debate about the merits of a newer biphasic approach (capacitation [CAPA]-IVM) versus standard IVM. At centres where it is used, CAPA-IVM has increased the maturation rate, and therefore the number of embryos available for transfer. However, there is a lack of data from large numbers of CAPA-IVM cycles, especially cumulative outcomes. Study design, size, duration This analysis included data from 1,563 individuals who underwent CAPA-IVM at a tertiary IVF center in Ho Chi Minh City, Vietnam from January 2016 to December 2023. Participants/materials, setting, methods All CAPA-IVM cycles in women with predicted excessive response (polycystic ovary syndrome or high antral follicle count) were included. Mean age was 29.6±3.5 years. Median duration of infertility was 3.3±2.5 years. CAPA-IVM was the first assisted reproductive technology in 90.5% of participants. Cumulative live birth rate was defined as the number of live births after using all embryos generated from a CAPA-IVM cycle. Main results and the role of chance Cumulative rates of clinical pregnancy, ongoing pregnancy and live birth were 54.9%, 44.4% and 37.8%, respectively. The median proportion of mature oocytes per cumulus-oocyte complex was 61.3% (IQR 50.0–73.3) and the median proportion of fertilized oocytes per cumulus-oocyte complex was 72.2% (IQR 55.6-85.7). The median total number of day-3 embryos per patient was 4.0 [IQR 3.0–7.0] and the total number of good day-3 embryos per patient was 3.0 [IQR 2.0–5.0]. The proportion of patients with no embryo was 5.2%. The number of frozen embryo transfer cycles was 1 (53.6% of patients), 2 (24.9%), 3 (7.0%), 4 (0.8%) or 5 (0.3%); 7.9% of patients had not undergone transfer of day-3 embryos at the time of analysis. Median [IQR] number of embryos and good embryos transferred was 2.0 [2.0–4.0] and 2.0 [1.0–2.0], respectively. No case of ovarian hyperstimulation syndrome recorded. Limitations, reasons for caution The characteristics of the study population (relatively young, lean women from Vietnam with predicted excessive response to ovarian stimulation) limit the external generalisability of the findings. Wider implications of the findings The cumulative live birth rate from all CAPA-IVM cycles performed in women with predicted excessive response at our centre was comparable to that of IVF. CAPA-IVM could be an alternative for this selected group of patients to avoid ovarian hyperstimulation. Trial registration number not applicable

O-211 Exploring risk factors of mismatch in the ART laboratory: An analysis based on 73719 electronic witnessing points

Abstract Study question What are the risk factors associated with mismatch (MM) and genuine mismatch (GMM) in the ART laboratory? Summary answer MM is associated with individual operators, oocyte denudation (OD) and embryo transfer (ET) processes, while GMM related to OD and extended work hours (>4pm). What is known already Mix-up of gametes or embryos in the ART laboratory causes dramatic consequences to both the patients and clinics. Recent studies using electronic witnessing system (EWS) equipped with radio frequency ID (RFID) tags, have revealed that most MM events only involved empty cell culture vessels, while the true mix-up risk arose from a subgroup of GMM involving culture vessels carrying gametes or embryos belonging to different patients. Exploration of risk factors associated with MM and GMM occurrence, separately, is still currently lacking in the literature. Study design, size, duration A total of 73719 witnessing points were retrospectively extracted from an EWS database, representing 11210 consecutive treatment cycles performed at Fertility North between January 2016 and July 2023. The 11210 treatment cycles comprised 5472 fresh IVF, 3732 frozen embryo transfer, 93 oocyte freeze, and 1913 intrauterine insemination cycles. Participants/materials, setting, methods All laboratory work areas were equipped with RFID readers. A MM was triggered by detection of RFID tagged cell culture vessels (either carrying biological material or not) and/or ID cards that belong to different patients in the same work area. A GMM was defined when a MM had involved biological materials and/or patients during procedure, with a potential mix-up. Risk factors evaluated included time of the day, weekdays, weekend, public holiday, operators, and laboratory processes. Main results and the role of chance A total of 138 (0.19%) MMs and 16 (0.02%) GMMs were identified during the study period, without actual mix-up. MM rate was the highest during 12-2pm (0.28%, p < 0.001) compared to other periods of the day, whilst GMM was the highest after 4pm (0.13%, p = 0.004). Neither MM nor GMM was associated with any specific weekday, weekend or public holiday (p > 0.05, respectively). Amongst 8 laboratory processes investigated, ET (0.36%, p < 0.001) led to the highest MM rate, followed by OD (0.35%, p = 0.021), but no increase was observed in oocyte collection, sperm preparation, insemination, embryo culture, cryopreservation and Assign ID. OD was the only process associated with higher GMM (0.13%, p < 0.001). Furthermore, Two of the 20 assessed operators were identified to produce more MMs (0.59%, p < 0.001, and 0.40%, p = 0.004; respectively) while GMM rates were similar among all operators (p > 0.05). Multivariate logistic regression indicated that the OD (adjusted odds ratio or aOR=2.147, p = 0.011) and ET (aOR=2.118, p < 0.001) processes as well as 2 individual operators (aOR=3.511, p < 0.001; aOR=2.538, p = 0.002; respectively) were independent risk factors to MM, but not the 12-2pm period of the day (aOR=1.341, p > 0.05). Finally, both extended work hours beyond 4pm (aOR=8.651, p = 0.005) and OD (aOR=9.538, p < 0.001) were independent risk factors to GMM. Limitations, reasons for caution Each individual ART laboratory has a unique team of scientists and workflow arrangement so findings in our study may not be universally applicable. GMM occurs at an extremely low frequency and is often calculated based on large numbers, therefore caution ought to be taken at statistical interpretation of data. Wider implications of the findings GMMs should be separated from MMs for analysis considering the very different clinical implications. Sufficient staffing with regular break and streamlined workflow are highlighted in preventing mix-up in the ART laboratory. Using electronically logged data, EWS enables identification of site-specific risk factors, which facilitates the development of corresponding preventative protocols. Trial registration number not applicable

P-642 The effect of oral dydrogesterone (DYD) on the hypothalamic-pituitary-ovarian (HPO) axis (gonadotropin and sex-steroid levels) and ovulation inhibition: a double-blind, phase I, randomized-controlled, parallel-group trial

Abstract Study question What is the effect of oral dydrogesterone (three cycles daily 20mg/30mg) on pituitary, ovarian and adrenal hormones, ovulation inhibition and endometrium in healthy ovulatory women? Summary answer Daily oral dydrogesterone, 20mg or 30mg, suppresses LH and inhibits ovulation in 33% and 73% of subjects, respectively, while not reducing E2 and other hormones. What is known already Dydrogesterone, a stereoisomer of progesterone, has high oral bioavailability and has demonstrated clinical utility in several indications, including endometriosis and assisted reproduction technologies. Progestin primed ovarian stimulation (PPOS) provides a cost effective and convenient alternative to the GnRH antagonist protocol to suppress a premature LH surge during ovarian stimulation in preparation for frozen embryo transfer IVF. In PPOS, studies have shown that dydrogesterone provides a comparable number of mature oocytes as a standard GnRH antagonist. The effects of various formulations and routes of administration of different progestins on sex hormones and the HPO has not been determined across the indications. Study design, size, duration A single-centre, double-blind, randomised, multiple-dose, parallel-group study of two doses of oral dydrogesterone over three 28-day treatment cycles: dydrogesterone 30mg, 10mg in the morning, afternoon and evening; dydrogesterone 20mg, afternoon dose replaced with placebo. The primary efficacy outcome was the number of subjects with “no ovulation at all” (Hoogland and Skouby score [HSS] 1-4) or “ovulation without pregnancy risk” (HSS 5-6 with negative Landgren criterion) recorded in all treatment cycles. Participants/materials, setting, methods The study population was 44 healthy, pre-menopausal women aged 18–35 years, with proven pre-treatment ovulation. The inclusion/exclusion criteria were defined to reflect the intended target population and the general contraindications for hormonal preparations. The primary objective was to compare the effect of the two self-administered doses of dydrogesterone on ovarian follicular growth leading to ovulation and E2 suppression. Secondary objectives included effect on other HPO hormones, the endometrium, PK characteristics and safety. Main results and the role of chance The number of responders to ovulation inhibition was dose-dependent: DYD 30mg, 72.7%, 95% CI: 49.78–89.27%; DYD 20mg, 33.3%, 95% CI: 14.59–56.97%. Based on HSS and Landgren criteria, there was 42.4% and 15.15% ovulation with pregnancy risk with the 20mg and 30mg doses, respectively. Neither dose had any clinically relevant influence on the average E2 concentration or FSH, androstenedione, dehydroepiandrosterone sulphate, testosterone and sex hormone binding globulin levels, while both doses suppressed the pre-ovulatory LH surge. Endometrial proliferation was mildly suppressed to a comparable extent with both daily doses. Hyperechogenic endometrium pattern was observed in 50% and 72% of treatment cycles in ovulating women in the 20mg and 30mg groups, respectively. Treatment with DYD did not significantly delay follicular growth or postpone ovulation in ovulating women. The more pronounced progesterone suppression with the higher 30mg dose may be due to the higher number of subjects without ovulation and thus without a post-ovulatory progesterone rise in that group. Return of ovulation after treatment cessation occurred in 91% women in the 42-day post-treatment period. The most frequently reported TEAE was ‘ovarian cyst’; all cases were of mild intensity and resolved at the end of the trial. No severe TEAE was reported. Limitations, reasons for caution Only two doses were studied in healthy, ovulatory women. DYD is used in various clinical contexts with concomitant other medications, such as gonadotropins for ovarian stimulation, or under luteotropic circumstances with human chorionic gonadotropin activity from exogenous or endogenous sources. Only limited morning PK sampling was performed. Wider implications of the findings Oral dydrogesterone used for endometriosis symptom reduction may be associated with a low risk of long-term adverse events from hypoestrogenism and suppression of androgens. Oral dydrogesterone displays relevant and short-term effects on LH levels, supporting its use in PPOS protocols. At therapeutic doses, dydrogesterone does not completely inhibit ovulation. Trial registration number EudraCT-No.: 2021-004747-24

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-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

O-024 Age affects ultrasound markers of endometrial receptivity in artificial cycles

Abstract Study question Are ultrasound markers of endometrial receptivity affected by patient age in artificial cycles? Summary answer Maternal age is linked to certain ultrasound markers such as a larger uterus, reduced endometrial compaction and lower uterine peristalsis. What is known already The decline in fertility in advanced age women has traditionally been linked to low oocyte quantity and quality. However, recent studies indicate that age may also affect endometrial aspects, influencing implantation and live birth rates. Advanced age can lead to impaired decidualization, increased fibrosis and decreased expression of progesterone and estradiol receptors. This study aims to investigate the influence of age on ultrasound factors related to implantation in patients undergoing embryo transfer in artificial cycles. Study design, size, duration Retrospective study of 452 patients undergoing frozen embryo transfer with artificial cycle, between January 2017 and December 2023. Participants/materials, setting, methods Ultrasound markers were evaluated, including assessment of uterine pathology, endometrial thickness before and after the onset of progesterone and uterine peristalsis. Serum progesterone level was also analysed. Spearman correlation and multivariate linear regression were used for analysis, adjusting for uterine factors. Subgroup analysis was performed for patients aged ≥45 years. Main results and the role of chance Age correlated inversely with endometrial compaction (S range: 0.3–0.2; p = 0.01) and uterine peristalsis (S range: −0.3–0.1; p < 0.001) and positively with uterus length (S range: 0.2–0.3; p < 0.001) and fibroids. Multivariate linear regression confirmed independent associations (R=.45; p < 0.001). Logistic regression in patients aged ≥45 revealed associations with uterine peristalsis (OR 0.7, 95%CI 0.5–0.9; p = 0.04) and uterus length (OR 1.03; 95%CI 1.01-1.06) but not with endometrial compaction (p = 0.103). Limitations, reasons for caution The main limitation of the study is its retrospective nature. Being a study based on daily clinical practice, the group of patients can be heterogeneous, which may have influenced the results. Studies with a homogeneous control group are needed to corroborate our findings. Wider implications of the findings Our findings indicate that advanced maternal age affects uterine ultrasound factors, potentially influencing endometrial receptivity in artificial treatments. This may be useful to inform patients of their prognosis and to perform better clinical counseling, as well as to explore different therapeutic strategies in older patients. Trial registration number not applicable

P-296 The relationship between serum HE4 and ultrasound findings of adenomyosis in infertility patients and its correlation with implantation and pregnancy outcomes in those undergoing IVF-ET

Abstract Study question Are there correlations between HE4 levels and the presence of ultrasonographic findings of adenomyosis in infertile women, and how does this relationship effect pregnancy outcomes? Summary answer The presence of subendometrial linear lines as marker of endo-myometrial invasion, is correlated with serum HE4 levels and negatively impacts pregnancy outcomes. What is known already Adenomyosis observed in women of reproductive age can present with infertility, particularly as implantation is adversely affected in junctional zone abnormalities. The endo-myometrial invasion in the pathogenesis of adenomyosis has been variously defined based on ultrasound criteria outlined in the MUSA (Morphological Uterus Sonographic Assessment) consensus. In patients with adenomyosis, while implantation rates may remain unchanged in some studies, an increased rate of first-trimester miscarriages has been reported in others. This study was conducted based on the hypothesis that HE4 (Human Epididymis Protein 4) marker may play a role in this potential invasiveness in adenomyosis and negatively affect embryo implantation. Study design, size, duration 82 infertile patients diagnosed with adenomyosis based on the MUSA consensus ultrasound criteria were included in our 10-month prospective study. HE4 testing was performed on serum samples collected from the patients. Our primary outcome focused on the association between ultrasonographic findings and the serum HE4 levels. The secondary outcomes comprised assessing the relationship between HE4 levels and the outcomes of implantation and pregnancy in the patients who underwent embryo transfer. Participants/materials, setting, methods In this study, infertile patients aged 20-40 diagnosed with adenomyosis via ultrasonography were included. Patients with a history of myoma or myomectomy, high-dose biotin intake, chronic organ failure, and a history of malignancy were excluded from the study. Ultrasonographic features were documented, and 39 patients underwent frozen embryo transfer. Pregnancy outcomes were categorized as clinical pregnancy or miscarriage for analysis. Main results and the role of chance As a primary outcome of the study, a statistically significant correlation between serum HE4 levels and subendometrial linear lines, as indicated in the MUSA consensus ultrasound criterias is found (p = 0.015). Logistic regression analysis showed that HE4 independently increased subendometrial linear striations [OR (95% CI) = 1.05 (1.01-1.10); model significance p = 0.020]. ROC analysis suggested that serum HE4 levels above the 37.4 pmol/L cut-off value may be associated with the presence of subendometrial linear striations. Although no relationship was found between HE4 levels and implantation rates, statistically significant higher levels of HE4 were observed in cases of miscarriage compared to ongoing pregnancies (p = 0.038). Limitations, reasons for caution Study limitations include reliance on 2D-TVUSG without 3D and Doppler. Enhanced evaluation using 3D-TVUSG and Doppler for JZ and subendometrial areas is recommended. Larger sample sizes could yield more impactful findings. Wider implications of the findings HE4 correlates with observed subendometrial linear lines, suggesting a link to endo-myometrial invasion. While it doesn’t impact transfer cycle implantation rates, it may be linked to higher early pregnancy losses. Trial registration number not applicable

P-160 Repeated treatment with the same sperm donor during the second cycle does not improve pregnancy rate, live birth rate nor risk of miscarriage

Abstract Study question Can repeated treatment with the same sperm donor in intrauterine insemination (IUI) and IVF/ICSI in the second cycle improve the outcome? Summary answer Pregnancy rate, live birth and miscarriage were not affected by repeated treatment with the same sperm donor in the second cycle with IUI or IVF/ICSI. What is known already Women with a longer exposure to paternal antigens have a higher chance of successful placentation and the use of donated gametes increases the risk for disorders related to placental insufficiency. Local exposure to seminal fluid has been shown to improve pregnancy rate. However, it is unknown how repeated exposure to the same donor, as opposed to changing donor, affects the outcome and currently there is no evidence suggesting that one method is superior to the other. Study design, size, duration This is a retrospective cohort study from three IVF clinics in Sweden including 868 women who have undergone reproductive treatments with donated sperms between 2014 and 2022. The outcomes pregnancy rate, live birth rate and risk of miscarriage were compared between women who had used the same donor in the second treatment cycle with women who were treated with a new donor. Participants/materials, setting, methods 631 nulliparous women undergoing IUI or IVF/ICSI with donated sperm using the same donor during two consecutive treatment cycles were compared to 237 nulliparous women who had changed donor between the treatments. All medical indications for treatment were included in the study. Oocyte donation cycles and frozen embryo transfer cycles were excluded. Statistical analyses were performed using logistic regression, adjusting for year of treatment, maternal age, treatment method and clinic. Main results and the role of chance No differences in pregnancy rate nor live birth rate were found when comparing repeated treatments with the same donor with change of donor in IUI or IVF/ICSI (odds ratio (OR); 0.95, 95% CI 0.67-1.34, p = 0.77; OR 1.30, 95% CI 0.86-1.95, p = 0.21 respectively). A significant difference was found in miscarriage (OR 0.38, 95% CI 0.18-0.79, p = 0.01). However, after adjusting for year of treatment, maternal age, treatment method and clinic, no significant differences were found in any of the outcomes: pregnancy rate (adjusted OR (aOR) 0.94, 95% CI 0.65-1.38, p = 0.77), live birth rate (aOR 1.21, 95% CI 0.78-1.88, p = 0.40) nor miscarriage (aOR 0.44, 95% CI 0.19-1.03, p = 0.06). Limitations, reasons for caution In addition to the retrospective study design, the restricted number of patients is a limitation. The possibility of undocumented confounders that could impact the results is also a reason for caution. Furthermore, as only two subsequent treatments were studied, any effect of longer exposure could not be evaluated. Wider implications of the findings Our results could not show that using the same sperm donor repeatedly is superior to changing donor regarding pregnancy, live birth or miscarriage. Further research on additional exposure to the same donor as well as outcomes specific to placental insufficiency is needed to address the issue further. Trial registration number NA

P-429 Measuring serum progesterone levels on the day of a fresh blastocyst transfer is debatable as there is no evidence for correlation with ongoing pregnancy results

Abstract Study question Does serum progesterone (P4) level on the day of a fresh blastocyst transfer relate to ongoing pregnancy rate (OPR)? Summary answer OPR after a fresh single blastocyst transfer seems not to be associated with serum P4 level on the day of transfer. What is known already Several studies have suggested an optimal serum P4 threshold for embryo transfers in frozen embryo transfer cycles. However, for fresh embryo transfers, data are scarce and conflicting. Study design, size, duration A retrospective single-center cohort study was performed on 598 complete data cycles, retained out of 631 consecutive fresh single blastocyst transfer cycles. Data were collected from patients undergoing a fresh IVF/ICSI cycle with autologous oocytes at a tertiary fertility center between June 2022 and August 2023. Participants/materials, setting, methods A total of 482 unique patients underwent one or more single fresh blastocyst transfers using micronized vaginal progesterone (MVP) 800mg BID for luteal phase support starting day after oocyte retrieval. Serum P4 levels were determined on day of transfer. The primary endpoint was OPR, positive hCG-test and early pregnancy loss (EPL) were secondary endpoints. Unadjusted and adjusted generalized estimating equations (GEE) assessed P4 level association with the endpoints, using an exchangeable working correlation matrix. Main results and the role of chance No association was identified between P4 levels on day of transfer and OPR after accounting for maternal age, blastocyst quality, P4 and estradiol level at last ultrasound, BMI and endometrial thickness. Data were grouped according to 10/50/90 and 25/50/75 percentiles, resulting in groups < = or > 27ng/ml and < = or > 40ng/ml, with omission of 90th and 75th percentile groups due to right-skewed distribution. With serum P4 levels higher than 40ng/ml, the probability of a positive hCG-test significantly increased (OR 1.79, CI 1.11-2.91; p = 0.018). No significant difference was observed in patients with serum P4 < = or > 27ng/ml (OR 1.23, CI 0.66-2.30; p = 0.506). Regarding OPR, no significant differences were observed when comparing patients with serum P4 < = or > 27/ng/ml or < = or > 40ng/ml (OR 0.88, CI 0.42-18.85; p = 0.736 and OR 1.41, CI 0.83-2.37; p = 0.203, respectively). Moreover, EPL did not significantly differ between serum P4 level groups (OR 1.93, CI 0.61-6.13; p = 0.265 and OR 1.2, CI 0.51-2.84; p = 0.674). Age (p < 0.001) and embryo quality (p < 0.001) are significantly related with OPR. Additionally, late follicular progesterone levels and OPR are significantly associated (OR 2.39, CI 1.16-4.95 in patients with P4 < = or > 27/ng/ml and OR 2.21, CI 1.07-4.55 in patients with < =40ng/ml and >40ng/ml). Limitations, reasons for caution Limitations include the retrospective design and the lack of live birth outcome data. Progesterone levels exceeding 60 ng/ml were not further analyzed to their precise value but grouped as 60 plus which did not allow to identify potential detrimental effects of very high P4 levels on treatment outcome. Wider implications of the findings Our data suggest that measuring P4 on the day of a single blastocyst transfer with MVP luteal phase support may not be indicative of OPR or the risk of EPL. This raises questions regarding the necessity for routine P4 measurements as well as the development of rescue strategies. Trial registration number ONZ-2023-0628

P-299 The influence of ovarian endometriomas surgery or not and the iron overload in follicular fluid on the outcome of IVF-ET

Abstract Study question To investigate the influence of ovarian endometriomas(OEM) surgery or not on the outcome of in vitro fertilization and embryo transfer. Summary answer Laparoscopic surgery can not significantly improve the outcome of IVF-ET in OEM patients, but may decrease the ovarian reserve. What is known already Despite the great advantages of ovarian endometriomas surgery treatment in endometriosis-linked infertility, the impact of laparoscopic cystectomy on outcomes of infertility management with ART is controversial. Numerous mechanisms have been proposed in an effort to delineate the multifaceted pathophysiology that induces impairment of reproductive dynamics in patients with OEM. Reactive oxygen species, dysregulation of the immune system and iron overload constitute the crucial mechanisms that detrimentally affect oocyte and embryo developmental potential. Study design, size, duration This study retrospectively included 882 cycles in our reproductive center from January 2018 to December 2020, and the patients were divided into operation group (n = 386) and OEM group (n = 496) according to whether they underwent laparoscopic cystectomy before IVF-ET. Participants/materials, setting, methods The baseline data of age, infertility duration, basic FSH, AFC, and BMI were used as matching factors, and Propensity score matching was carried out according to the sample ratio of 1:1, and 327 cycles in the operation group and 327 cycles in the OEM group were finally included. Follicular fluid was collected under ultrasound guidance during oocyte retrieval. A total of 74 follicular fluid samples meeting the study conditions were collected. Main results and the role of chance (1)The clinical pregnancy rate of fresh embryo transfer cycle in the OEM group was significantly higher than that in the operation group (77.4% Vs 52.9%), and the difference was statistically significant (P = 0.039). There was no significant difference in pregnancy outcome in frozen embryo transfer cycle (P > 0.05). (2) The results of Multi-factor logistic regression model showed the clinical pregnancy rate of patients in the OEM group was 3.048 times than that of patients in the operation group in fresh cycle, and the difference was significant (OR 3.029 95%CI 1.017-9.018, P = 0.047), while early abortion and live birth pregnancy outcomes were not significantly affected in both groups. For the frozen embryo transfer cycle, there were no significant effects on clinical pregnancy, early abortion and live birth pregnancy outcomes in both groups. (3) There was no significant difference in follicular fluid iron concentration between OEM group and control group(11.53±3.38 Vs 12.18±4.37μg/dl, P = 0.112). The concentration of ferritin in follicle fluid in OEM group (57.38±139.90) was significantly higher than that in control group (24.88±13.76 μg/ml), the difference was statistically significant (P = 0.032). Limitations, reasons for caution The present study being of a retrospective and monocentric study, may not come to a very convincing conclusion, and some unknown biases might still exist due to possible underestimation of some confounders. Wider implications of the findings Collectively, our results indicate that laparoscopic ovarian cystectomy couldn’t significantly improve the IVF-ET outcomes in patients with OEM, but rather increased the risk of reduced ovarian reserve function. Ovarian reserve function was the main factor affecting the IVF-ET outcomes for infertile patients with OEM. Trial registration number /