Fresh Embryo Research Articles

O-043 Con

Abstract Dual and/or double trigger improve IVF success - CON The improvement of in vitro fertilization (IVF) outcomes remains a pivotal area of reproductive medicine research, with the dual trigger approach emerging as a significant innovation. This con abstract explores the scientific basis, methodology, and outcomes associated with the dual trigger strategy, juxtaposed with conventional triggering methods in IVF protocols. The dual trigger, incorporating both Gonadotropin-Releasing Hormone Agonist (GnRHa) and Human Chorionic Gonadotropin (hCG), has been posited to improve oocyte maturation, retrieval-, and live birth rates. By scrutinizing recent studies, clinical trials, and meta-analyses, this debate aims to delineate the efficacy, safety, and application scope of this approach. Initial investigations into the dual trigger method have highlighted its potential to ameliorate oocyte quality and maturity, which are crucial determinants of IVF success. The mechanism underlying this improvement involves the simultaneous activation of LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone) receptors, enhancing follicular response and oocyte developmental competence. Studies have demonstrated an increase in the number of mature oocytes retrieved, attributed to the more synchronized and comprehensive follicular stimulation afforded by the dual trigger. This augmentation in oocyte quality and quantity directly correlates with enhanced embryo development profiles, and higher implantation and clinical pregnancy rates. Furthermore, the dual trigger method has shown promise in reducing the incidence of Ovarian Hyperstimulation Syndrome (OHSS), a severe complication of IVF treatments. By leveraging the luteolytic effects of GnRHa, this strategy minimizes the risk associated with exogenous hCG administration, thus offering a safer alternative for patients predisposed to OHSS. The application of the dual trigger in specific patient cohorts, such as those with PCOS or poor ovarian responders, has been underlined, indicating its potential for personalized reproductive medicine. However, the implementation of the dual trigger strategy is not without challenges. Variability in patient response necessitates a highly individualized approach, with precise dosing and timing adjustments to optimize outcomes. The existing literature presents a heterogeneity in study designs, populations, and outcome measures, which complicates the direct comparison of dual trigger efficacy against traditional methods. Furthermore, the long-term safety and potential impacts on offspring warrant further investigation, given the recent adoption of this approach. In conclusion, the dual trigger strategy may offer significant benefits in enhancing IVF outcomes. Its potential to improve oocyte maturity and quality could increase the number of retrievable oocytes and reduce the incidence of OHSS. However, it is important to acknowledge that, while the GnRH agonist trigger combined with a freeze-all strategy eliminates the risk of OHSS in women with PCOS, the dual trigger approach followed by fresh embryo transfer does not. Further research is imperative to refine its application, understand its mechanisms fully, and establish comprehensive guidelines for its use. The promise of the dual trigger approach underscores the importance of continuous innovation and evidence-based practices in enhancing the efficacy and safety of IVF treatments.

P-583 The ploidy status in blastocysts generated from progestin primed ovarian stimulation and GnRH antagonist protocols: A comparison of 14.000 trophectoderm biopsies

Abstract Study question Is there any difference in the euploidy rate in a large cohort of blastocysts when produced after a progestin-primed or GnRH antagonist protocol? Summary answer Euploidy rates in trophectoderm biopsies when tested with next-generation sequencing (NGS) were similar after progestin-primed or GnRH antagonist protocol. What is known already Preimplantation genetic testing (PGT) might be employed in patients with advanced female age to improve efficiency of embryo transfer. Given the fact that there is no fresh embryo transfer in that policy, progestin primed ovarian stimulation (PPOS) protocol might be preferred over GnRH analogs due to its lower cost and advantage of oral administration instead of s.c injections. However, due to small sample sizes within the limited number of studies, there is lack of consensus whether ploidy status might be affected when an embryo is generated after a PPOS or GnRH analogs protocol. Study design, size, duration A retrospective cohort study was designed among patients that has undergone in-vitro fertilization (IVF) treatment between January-2018 and June-2023 in Bahceci Health Group. For the aim of PGT, only patients treated with PPOS or GnRH antagonists were included. PPOS protocol referred to utilization of either medroxyprogesterone acetate (10 mg/day) or dydrogesterone (20-30 mg/day) to avoid premature ovulation during ovarian stimulation. In GnRH antagonist protocol, flexible or fixed approach was preferred for pituitary suppression. Participants/materials, setting, methods During the study period, 11.616 and 2.480 trophectoderm biopsies had been performed from blastocysts (D5/6) generated after GnRH antagonist or PPOS protocol, respectively. Of them, 9.390 and 1.801 of them were analyzed with NGS. A total of 303 (3.2%) and 17 (0.9%) biopsies were excluded due to failure or non-informative results after testing. For the final analysis, 9.087 and 1.784 biopsies were included in the antagonist and PPOS arms for the current study. Main results and the role of chance The mean age of women treated with GnRH antagonist and PPOS was comparable (36.5±5.3 vs. 36.7±5.4 years, p = 0.17). The respective numbers of euploid embryos were 3.912 and 1.784. Per biopsied embryos, the rate of euploidy was 33.7% and 34.8% (p = 0.30). The rate of euploidy per metaphase II oocyte and 2-PN were 10.6% and 13.5% in the GnRH antagonist arm and they were 11.3% and 14.4% in the PPOS arm (p = 0.08 and p = 0.07) without any statistical significance. When only patients included in whom all available blastocysts were biopsied, the linear regression model revealed only female age (RR: -0.32 CI%95: -0.38 to – 0.26, p < 0.001) as the independent factor for the prediction of ploidy rate (euploid/euploid + aneuploid embryos) when body mass index, duration of infertility, AMH, number of oocytes, number of metaphase-II oocytes, and the type of ovarian stimulation protocol were entered into the model. This model represented female age as the sole independent factor (RR: -0.14 CI%95: -0.18 to – 0.11, p < 0.001) when euploidy rate per 2PN was tested with the same variables. Limitations, reasons for caution The inherent risks cannot be excluded due to the retrospective nature of the current study. Wider implications of the findings The current study includes the largest number of trophectoderm biopsies generated from PPOS and GnRH antagonist protocol, giving the opportunity to compare them with each other. Due to lack of any superiority of one protocol regarding ploidy status, financial cost and easiness might favor PPOS when PGT is planned. Trial registration number None

P-577 A randomized trial to compare the live birth rate following the progestin-primed ovarian stimulation versus the antagonist protocol in women with anticipated high ovarian responses

Abstract Study question Is there difference in the live birth rate following the progestin-primed ovarian stimulation (PPOS) versus the antagonist protocol in women with anticipated high ovarian responses? Summary answer The live birth rates of the first frozen embryo transfer following PPOS and the antagonist protocol were comparable in women with anticipated high ovarian responses. What is known already Progestin when given orally inhibits the pituitary LH surge during ovarian stimulation when taken orally i.e. progestin-primed ovarian stimulation. Two randomized trials showed similar number of oocytes for PPOS and the antagonist protocol in oocyte donation cycles. However, there is still no randomized trial to compare the live birth rate between PPOS and the antagonist protocol. Study design, size, duration This is a randomized controlled trial of 784 infertile women conducted from June 2020 and October 2021. Participants/materials, setting, methods Infertile women aged <43 years undergoing the first IVF cycle in a tertiary fertility center and having antral follicle count >15 randomly assigned in a 1:1 ratio into two groups: PPOS group and the antagonist group. Medroxyprogesterone 10 mg daily was given from the start of ovarian stimulation until the day of ovulation trigger in the PPOS group. The primary outcome was the live birth rate of the first frozen embryo transfer. Main results and the role of chance 784 women were randomly assigned into two groups: PPOS group (n = 392) and antagonist group (n = 392). Embryo transfer was either cancelled or postponed in 62 (62/392, 15.8%) women in the PPOS group and 65 (65/392, 16.6%) in the antagonist group because of no transferable embryos or no frozen embryo transfer within 6 months following randomization. The two groups were similar in demographic characteristics and number of oocytes obtained/fertilized, the number of cleaving embryos, number of good quality embryos at day 3, number of blastocysts developed and number of embryo/blastocyst frozen. There was no statistically significant difference in the live birth rate of the first frozen embryo transfer cycle between the progestin-primed ovarian stimulation and antagonist groups based on both intention to treat [37.5.0% (147/392) versus 32.7% (128/392), RR 1.148 (95% CI = 0.949–1.390), P = 0.16] and per protocol analysis [44.5% (147/330) versus 39.1.% (128/327), RR 1.138 (95%CI = 0.950–1.364), P = 0.16]. Both groups showed comparable clinical pregnancy, ongoing pregnancy, miscarriage, multiple pregnancy, ectopic pregnancy and cumulative live birth rates. Limitations, reasons for caution Women with anticipated high ovarian responses were recruited and the results may not be extrapolated to the general population seeking IVF. This is not a blind study although the live birth rate as the primary outcome is objection. The duration of the study is 6 months since randomization. Wider implications of the findings In situations in which fresh embryo transfer is not required such as oocyte/embryo freezing for fertility preservation, oocyte donation or preimplantation genetic testing, the PPOS protocol may be preferred over the antagonist protocol. Trial registration number NCT04414761

O-018 Utilisation of second successive ejaculate as a way to overcome poor semen parameters for couples who wish to undergo conventional-IVF

Abstract Study question Can a second successive-ejaculate (SSE) be an option for patients with poor sperm parameters (PSPs) on ovum pick-up (OPU)-day who prefer to undergo conventional-IVF (c-IVF)? Summary answer SSE can be a valid option for patients with PSPs who do not wish to undergo ICSI as an assisted reproductive technology (ART) treatment. What is known already ART is applied when first-line treatment for infertility (timed intercourse or intrauterine insemination) is unsuccessful. The male partner is requested to follow ejaculatory abstinence, which according to the WHO guidelines is 2-7 days, while ESHRE recommends 3-4 days. Among these couples there are cases that require ICSI due to semen analysis with PSPs on the day of OPU. However, some couples are reluctant to undergo ICSI and prefer c-IVF as a treatment method. For those cases, we request a second semen sample on the same day (time interval: 1-4 h) and c-IVF is performed using the two ejaculates combined. Study design, size, duration This is a single-centre retrospective study employing 212 semen from male partners with PSPs in the first semen collection on the OPU-day and subsequently, an SSE was requested in order to perform c-IVF according to patients’ wishes. The data were collected from May 2006 to October 2023 in our clinic (SSE-group). The Control group included 271 semen samples from men where c-IVF was conducted using one ejaculate from January to December 2021 in our clinic. Participants/materials, setting, methods The sperm parameters were analysed according to the WHO manual for the examination and processing of human semen and compared between the first and second ejaculates in the SSE-group. Fertilisation rate (FR), percentage of clinically utilised embryos and clinical pregnancy rate were compared between the SSE-group and the Control group. The SSE-group had 254 ART-cycles and the mean maternal age was 36.8±4.9y.o. The Control group included 432 ART-cycles and the mean maternal age was 38.1±5.2y.o. Main results and the role of chance In SSE-group the semen volume of the first ejaculate was significantly higher compared to the second ejaculate (P< 0.0001). The sperm concentration and sperm motility were significantly higher in the second ejaculate compared to the first one (P<0.0001). In the same fashion, the total-motile sperm-count was significantly higher in the second ejaculate compared to the first (P=0.01). All the semen parameters in the Control group were significantly higher compared to both first and second ejaculates from the SSE-group (P<0.00001). The normal FR was significantly higher in the Control group compared to the SSE–group (P<0.01). On the other hand, there was no significant difference in the percentage of embryos that could be utilized (cryopreserved + freshly-transferred) between the two groups (P=0.218). Pregnancy rate for fresh embryo transfers (ETs) was significantly higher in the SSE-group compared to the Control (P=0.005), while there was no significant difference between the two groups for pregnancy rate for frozen/thawed ETs (P=0.728). The main strength of our study is that the utilisation of the SSE combined with the first ejaculate did not decrease the pregnancy rate for the couples with PSPs that wished to follow c-IVF as their treatment and it could actually provide an effective option for them. Limitations, reasons for caution SSE may improve the sperm parameters and give the opportunity to infertile couples to undergo c-IVF according to their wish. However, since the FR was lower in the SSE-group, it is of paramount importance to provide sufficient explanation to those couples and obtain their consent when requesting an SSE. Wider implications of the findings Overall, SSE had positive effect to a large number of parameters evaluated in this study. Additionally, the rate of utilised embryos was similar between the two groups. Two successive-ejaculates combined can be employed without any negative impact for couples with PSPs on the OPU-day that are reluctant to undergo ICSI. Trial registration number not applicable

P-772 Assisted reproductive technology and the risk of minor congenital heart defects in the newborn

Abstract Study question Are children conceived through assisted reproductive technology (ART) at higher risk of minor congenital heart defects (CHD) compared with naturally conceived (NC) children? Summary answer Contrary to previous studies children conceived through ART had similar risk of minor CHDs compared with children conceived naturally. What is known already Congenital heart defects (CHD) may precipitate cardiac arrhythmias, lead to thromboembolic events, culminate in heart failure or even sudden cardiac demise. A systematic review and meta-analysis showed an elevated odds ratio (OR) for diagnosis of any CHD among children conceived through in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) compared with NC children. Other studies indicate that ART is associated with an increased arterial blood pressure and vascular dysfunction in the pulmonary and systemic arterial vasculature. This association persists throughout childhood, adolescence, and early adulthood in individuals conceived through ART; this indicates a lasting impact on the cardiovascular circulatory system. Study design, size, duration The present study is a sub-study to the Copenhagen Baby Heart Study (CBHS), a prospective population-based cohort study of > 25 000 children born in the three main maternity wards in Copenhagen, Denmark, in 2016–2018. Transthoracic echocardiography (TTE) was performed on all children within 60 days of delivery and diagnosis of CHD was reviewed by a specialist in paediatric cardiology. Information regarding parental health, pregnancy, delivery, and the newborn was collected through Danish patient registries. Participants/materials, setting, methods This study includes all children conceived by ART in the CBHS (n = 1 784), and a matched group (1:4 by maternal age at birth) of NC children (n = 7 141). Exclusion criteria were genetic or chromosomal syndromes and heart surgery. Minor CHD was defined as an atrial (ASD) or ventricular septum defects (VSD), bicuspid aortic valve, coarctation of the aorta, pulmonary stenosis, or patent ductus arteriosus. We calculated ORs using logistic regression analyses. Main results and the role of chance The mean maternal age at birth was 34.9 (standard deviation [SD] ±4.4) and 35.1 years (SD ± 4.6) and the newborn mean age at TTE was 12.1 (SD ± 9.3) and 12.2 days (SD ± 9.4) in the ART and NC population, respectively. Parental CHD was registered in 40 (2.2 %) children in the ART group and 121 (1.7 %) in the NC group. Overall, 165 (9.2%) children conceived by ART and 611 (8.6%) NC children were diagnosed with a minor CHD. The most prevalent CHDs were VSD and ASD which accounted for 38.8 % and 35.2 % in children with CHD in the ART group, respectively, and 36.8 % and 33.9 % in children with CHD in the NC group. The unadjusted OR for minor CHD was 1.09 (95% CI 0.91–1.30). Adjustments for maternal age and parental CHD did not change the OR. There were no differences in ORs when stratifying by minor CHD type. We stratified by the method of ART: ICSI and IVF and frozen embryo transfer and fresh embryo transfer, and calculated risk of minor CHD comparing the methods and with NC children. We found no difference in any ORs, crude or adjusted. Limitations, reasons for caution Children born preterm, and children with severe minor and major CHDs, were underrepresented in the cohort indicating parents of such children chose not to participate in a research project that would include another hospital visit. Residual confounding is plausible because parental CHD diagnoses were retrieved from patient registries. Wider implications of the findings The number of children conceived through ART is increasing each year and previous research have found an increased risk of CHD in children conceived through ART. Our findings indicate no increased risk of minor CHD, providing comforting and significant information for advising individuals considering or undergoing ART treatment. Trial registration number NCT02753348

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 /

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

O-090 The paradox of choice in double (DET) versus single (SET) embryo transfer: more is less!

Abstract Study question Do couples with two blastocysts opting for DET have a better outcome than those with SET, freezing of the second and eventually subsequent second SET? Summary answer More children are born after 2x SET with the overwhelming majority (96.3%) of these children being singletons, whereas after 1x DET 49.5% are multiples What is known already According to the most recent publication of the European IVF Monitoring Consortium, in 33 European countries reporting data on these topics SET is performed in 55.4% of fresh transfers whereas in the other cycles, two, three and even 4 or more embryos are transferred, often resulting in twin or higher order multiple pregnancies, but there is no information on the duration of culture and number of embryos available in these cycles. The German IVF-Registry (D·I·R) has collected more than 2.4 million datasets from German ART clinics since 1997 and has access to these data and other relevant patient characteristics. Study design, size, duration Retrospective real-world data analysis from 140 German IVF-centers collected by the German IVF-Registry (D·I·R) between 2017 and 2021. Data were collected prospectively, controlled for plausibility, and evaluated anonymously. Treatment cycles from four years between January 1st, 2017 and December 31st, 2020 were evaluated. Pregnancy outcome was monitored until end of 2021. All couples having at least 2 blastocysts available for fresh transfer in their 1st treatment cycle were identified and included in the analysis. Participants/materials, setting, methods 19,702 women with similar characteristics (i.e. first cycle of IVF or ICSI, fresh embryo transfer, two blastocysts available on the day of fresh ET, signed consent to freeze supernumerous 2PN or embryos) were stratified into two groups. Therapy results after 1x DET (fresh) vs. 1x SET (fresh) plus 1x SET (frozen-thawed) were evaluated for clinical pregnancy rates, life birth rates, number and order of multiple pregnancies, multiple deliveries, and total number of children born. Main results and the role of chance From 19,702 women meeting the inclusion criteria, 9,643 (48.9%) had a DET and 10,059 (51.1%) had a SET. The age of patients in both groups was not significantly different (DET: 34.1y vs. SET: 33.7y). As expected, ongoing pregnancy rate (OPR) and life birth rate (LBR) after DET were higher compared to SET (OPR: 49.4% vs. 42.3%; LBR 38.5% vs. 33.1%). Those opting for SET however had the chance of a second SET with the frozen-thawed blastocyst and so far, from 7,207 women who started the frozen embryo transfer cycle (FET), 6,431 had the second blastocyst transferred with a CPR of 29.5% and LBR of 19.4% per started FET. After DET, only 67.4% of deliveries were singletons. Of the 32.6% multiples, 97.4% were twins, 2.5% triplets and 0.1% quadruplets. After fresh (or frozen) SET, 98.4% (97.6%) of deliveries were singletons, the remaining were solely twins (1.6% (2.4%)) and no higher order multiples. Per 1,000 women having a DET, 514 children were born and 49.5% of those were either twins, triplets or quadruplets. Per 1,000 women after 2x SET, more children were born (536), and only 3.7% of those were twins, no triplets or quadruplets. Limitations, reasons for caution In this retrospective analysis, the reasons of the couples for the decision of having SET or DET is not known. One potential bias caused by the additional costs for freezing/thawing (not reimbursable in Germany) can be excluded (only those having opted to freeze supernumerous 2PN or embryos were evaluated). Wider implications of the findings Couples undergoing IVF understandably want to maximize their chances of success, sometimes opting for a DET, underestimating the number of multiples and neglecting the risks. We clearly show that after DET every second child is a twin, triplet or quadruplet, and even more children are born after two successive SETs. Trial registration number not applicable

P-147 Number of autologous mature oocytes as a predictor of live birth rate in women aged over 40 who do not accept egg donation

Abstract Study question Is the number of mature oocytes (M2) retrieved a reliable predictor of success for women aged over 40 with autologous oocytes? Summary answer 79.5% of live births were achieved in patients with ≥3M2 retrieved, 14.3% in women with 2M2, and 6.5% in women with 1M2. What is known already The delayed desire for parenthood has become a social phenomenon, particularly among women over 35. Reproductive outcomes in women over 40, using their own oocytes, are usually poor due to a decrease in follicle and oocyte quantity and quality, along with an increased prevalence of oocyte chromosomal abnormalities. While using donated oocytes is often recommended, it remains an unacceptable option for many couples. Furthermore, in Argentina the legislation on Assisted Reproduction Technologies endorses assisted reproductive treatments employing womeńs own oocytes up to the age of forty-four. Study design, size, duration This retrospective observational study, was performed between January 2004 and December 2022 in 5757 patients aged 40 and above undergoing autologous oocyte retrieval and fresh embryo transfer because they do not accept PGTa. Statistical analysis was performed using the InStat GraphPad statistical package. One-way ANOVA and two-tailed Student’s t-test were performed as required. Participants/materials, setting, methods Group1(G1): 40 years (N = 1600); Group 2(G2): 41years (N = 1300); Group 3(G3): 42 years (N = 1087); Group 4(G4): 43 years (N = 735); Group 5(G5): 44 years (N = 496); Group 6(G6): 45 years (N = 302); Group 7(G7): 46 years (N = 140); Group 8(G8): 47 years (N = 61); Group 9(G9): 48 years (N = 23); Group 10(G10): 49 years (N = 13). Primary outcome was relationship between number of M2 and live birth rate. Secondary outcomes were live birth rate, cancellation rate, miscarriage rate, clinical pregnancy rate. Main results and the role of chance Number of M2 retrieved: G1=3.9±3.4 [1-16]; G2=3.6±2.7 [1-14]; G3= 3.5±2.3 [1-12]; G4= 3.4±2.8 [1-14], G5=2.5±1.5 [1-7]; G6=2.3±2.2 [1-12]; G7=1.8±1.5 [1-8]; G8=1.5±0.9 [1-3]; G9=1.3±0.6 [1-3]; G10=1.0±0 [1-1]. Cancelation rate (%): G1=18.2 (292/1600); G2=20.9(272/1300), G3=22.3(243/1087); Gr4= 29.9(220/735); G5=28.0(139/496); G6=38.1 (115/302); G7= 42.8(60/140); G8= 44.3 (27/61); G9=47.8 (11/23); G10= 61.5 (8/13). Clinical pregnancy/transfer rate(%): G1=24.2 (316/1308); G2=21.7 (223/1028); G3=18.0(152/844); G4=18.0 (93/515); G5=9.2 (33/357); G6=11.2 (21/187); G7=3.7 (3/80); G8=0 (0/34); G9=8.3 (1/12); G10=0 (0/5). Live birth rate (%): G1= 11.8 (147/1250); G2= 10.0 (99/993); G3= 6.8 (57/831); G4= 6.6 (34/515); G5= 3.2 (11/348); G6= 2.1 (4/187); G7= 1.2 (1/80); G8= 0 (0/34); G9=0 (0/12); G10=0 (0/5). Miscarriage rate (%) 40 to 46 years: G1= 43.0 (111/258); G2= 47.3 (89/188); G3= 59.0 (82/139); G4= 63.4 (59/93); G5= 66.7 (22/33); G6= 80.9 (17/21); G7=66.7 (2/3) and 100 (1/1) for 48 years (G9). Cancellation rates increased with age. The number of M2 retrieved was significantly associated with clinical pregnancy, live birth and miscarriage rates. The average number of mature oocytes retrieved in cases resulting in live births was consistently higher across all age groups: G1=5.8±2.7 [1-16]***; G2= 4.8±3.5 [1-14]***; G3= 4.0±2.1 [1-9]***; G4= 5.7±2.7 [3-13]***; G5= 4.2±1.4 [2-7]***; G7= 6.0±1.4 [5-8]***; G8= 7.0±0 [7,7]*** (***= p < 0.0001). Limitations, reasons for caution This extensive retrospective study’s conclusions should be cautiously applied, limited to a specific group of elderly women unwilling to consider egg donation. 106 clinical pregnancies were not included because we did not have information on live births. Wider implications of the findings Identifying parameters associated with higher live birth rates in this population may aid in providing realistic expectations for achieving pregnancy with autologous oocytes. This information could guide medical advice and potentially suggest alternative options, such as egg donation or adoption. Trial registration number NOT APPLICABLE

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

P-310 Impact of adenomyosis on the live birth rate during management by in vitro fertilization : a French study

Abstract Study question Evaluate the impact of adenomyosis on the likelihood of live birth after a fresh embryo transfer. Summary answer Adenomyosis reduces the live-birth rate. The location of adenomyosis and the type of protocol appears to have no impact on the live birth rates. What is known already The prevalence of adenomyosis varies between 7 and 27%, and affects 25% of infertile women. Its impact on fertility remains debated. According to some studies, it leads to a lower pregnancy rate, a doubling of the spontaneous miscarriage rate and a lower live birth rate as compared to non-adenomyosis women. However according to some authors adenomyosis does not reduce the live birth rate. Similarly, the impact of the location of adenomyosis remains debated. On the impact of the stimulation protocol, several studies have shown that the use of GnRH agonist improves the live birth rate in patients with adenomyosis. Study design, size, duration This is a retrospective, descriptive and observational study, managed at the fertility department of Dijon University Hospital between January 2015 and March 2020. Systematically, the women infertility cause was assessed. We compared the group of patients with adenomyosis (i.e. symptomatic adenomyosis completed with a 3D ultrasound within a maximum of 1 year prior to management) with controls (i.e. patients treated for another cause of infertility). Ultrasound was performed by the same two experienced operators. Participants/materials, setting, methods We included 340 patients aged 18-41 years. Data concerning live births and type of stimulation protocol were collected from the patient’s electronic medical and therapeutic records. MUSA classification was used to determine whether the adenomyosis was localized or diffuse. The primary endpoint of this study was the live-birth rate (LBR) after fresh embryo transfer. The implantation and miscarriage rates were also compared. Main results and the role of chance We included 92 patients in adenomyosis group, and 248 patients in control group. Baseline characteristics of patients including women age, BMI and smoking habits were comparable in both groups. Moreover, no difference was found on the mean number of mature oocytes and embryos between the two groups. LBR after fresh embryo transfer was significantly lower in the adenomyosis group than in the control (34.8 % versus 41.5%, respectively, p = 0,02). There was no significant difference in implantation rate (35.7% versus 37,4%, p = 0.76). Early miscarriage rate (<12 weeks of amenorrhea) was higher in the control group than the adenomyosis group (15.3 versus 7.5, p = 0.012). Concerning late miscarriage (>12 weeks of amenorrhea), we observed 3 medical termination of pregnancy (all for fetal malformation) and 1 miscarriage (10%) in the adenomyosis group and 1 miscarriage (0.81%) in the control group (p = 0.02). Subgroup analyses showed no decrease in LBR according to adenomyosis location (32.7% versus 37.2% in the diffuse and localized groups, respectively, p = 0.46). Limitations, reasons for caution Even though our cohort is a good reflection of the all-French population of Burgundy since all patients are treated at the fertility center of Dijon. Despite its retrospective nature and the small number of included adenomyosis-patients, the ultrasound scans were performed by two experienced operators that reduced inter-observer variability. Wider implications of the findings It would be useful to carry out a prospective study including more patients to better assess the impact of location on implantation. It would also be interesting to evaluate neonatal and obstetrical complications, especially the late miscarriage issue requiring further investigation. Trial registration number non-clinical trials

P-421 Enhancing the success of frozen embryo transfer by human chorionic gonadotropin injection on the day of progesterone supplementation onset - a machine learning study

Abstract Study question Does subcutaneous injection of human chorionic gonadotropin (hCG) at the onset of progesterone supplementation affect clinical pregnancy rate in frozen embryo transfer cycles? Summary answer Clinical pregnancy rates are higher when hCG injection is administered at the onset of 300 mg/day progesterone in patients undergoing frozen embryo transfer. What is known already HCG and progesterone play crucial roles in embryo transfer and implantation during in vitro fertilization. Exisitng studies have demonstrated that pre-administration of hCG at the onset of progesterone supplementation for frozen embryo transfer increases clinical pregnancy rates in patients with endometriosis. However, the synergistic effects of hCG and progesterone co-supplementation in a broader range of patients remain unexplored and require further investigation. A multifactorial analysis of hormone replacement therapy, covering various patient-specific aspects, is necessary to understand the implications of this approach. Study design, size, duration This retrospective cohort study analyzed data from 2,251 single frozen embryo transfers performed between Jan 2019-Aug 2023 at the INVICTA Fertility Centre, Poland. The dataset was selected by the practitioner and included age, AMH, BMI, embryo morphology grade, total number of transfers, medical and embryological procedures, recurrent implantation failure, preimplantation genetic testing, endometrial thickness before transfer (≥ 7 mm), and the menstrual cycle day on which progesterone was started. Participants/materials, setting, methods Patients (21-47 years) receiving 300 or 600 mg/day progesterone for five days were divided into the control and hCG (6,500 IU hCG injection on progesterone onset) groups. A machine learning model was trained using a gradient boosting technique (100 decision trees, four leaves, maximum depth of two nodes, learning rate of 0.05) to identify factors affecting the clinical pregnancy rate. Statistical analysis was performed to compare clinical pregnancy rates between the groups. Main results and the role of chance Our machine-learning model revealed that hCG injection (512 processes vs. 1739 processes without it) at the onset of progesterone administration is an important feature for the clinical pregnancy rate. The performance accuracy of the model was approximately 70%. Of the 1,294 protocols where patients received 300 mg/day progesterone, 311 included hCG injection while 983 did not. The clinical pregnancy rate was significantly higher in the hCG group than that in the control group (54% vs. 46%, P < 0.05), with 167 clinical pregnancies observed in patients receiving hCG injections against 452 pregnancies without it. In contrast, among the 957 protocols where 600 mg/day progesterone was administered, the previously observed effect was not significant (P > 0.05). Comparing 201 processes with hCG injection to 756 processes without it, the incidence of clinical pregnancies was 46.8% and 47.2% (with 94 and 357 confirmed pregnancies), respectively. Other factors such as the morphology grade of the embryo used for transfer, patient’s age, AMH, BMI, total number of transfers performed on the patient, menstrual cycle day on which progesterone was started, occurrence of recurrent implantation failure, and the use of preimplantation genetic testing were not significantly different between the groups. Limitations, reasons for caution This study focused on frozen embryo transfers and validation across other protocols using fresh embryo transfers, and different doses or routes of hCG and progesterone administration are needed. The impact of hCG administration on patients with various causes of infertility should also be explored. Wider implications of the findings Pre-administration of hCG injection along with a daily dose of 300 mg/day progesterone enhanced clinical pregnancy rates for frozen embryo transfer. This holds the potential for the optimization of hormon supplementation protocols to increase overall success rates in assisted reproductive technologies. Trial registration number not applicable

P-311 Impact of adenomyosis on reproductive outcomes applying the revised Morphological Uterus Sonographic Assessment criteria in fresh donor oocyte recipients pretreated with GnRH agonist

Abstract Study question Could the diagnosis of adenomyosis (AD) impact reproductive outcomes when applying the revised Morphological Uterus Sonographic Assessment (MUSA) criteria in fresh donor oocyte cycles? Summary answer Adenomyosis diagnosis following the revised MUSA criteria in recipients did not have adversely affect reproductive outcomes in fresh donor oocyte recipients pretreated with GnRH agonist What is known already Prior metanalysis on IVF outcomes in patients with adenomyosis suggested lower clinical pregnancy and live birth rates, and increased miscarriage rates. Some studies suggest improved pregnancy rates with ultra-long GnRH agonist pretreatment. Most studies focused on autologous embryo transfer without euploidy confirmation, and diagnostic criteria lacked consensus, in 2021 MUSA redefined criteria distinguishing direct and indirect features with different implications. Study design, size, duration A retrospective cohort study included all fresh oocyte donation cycles from January 2014 to September 2023, evaluating adenomyosis impact on implantation rate, clinical pregnancy rate, miscarriage rate, ectopic pregnancy rate. The study analyzed 252 cycles without a formal sample size calculation due to its retrospective nature. Participants/materials, setting, methods The study included 252 first fresh oocyte reception cycle with a fresh embryo transfer. Severe male factor cases were excluded. A transvaginal ultrasound (TUS) screening for adenomyosis criteria was performed, diagnosis required at least two criteria, with one being direct. Endometrial preparation involved one dose of 3,75mg triptorelin acetate intramuscularly injected in mid luteal phase, to facilitate the synchronization with donor and estradiol patches. Main results and the role of chance Adenomyosis was diagnosed in 10,7% (AD), endometriosis (END) was present in 21,8 % and 26,6% of patients presented both diagnoses. Endometriosis patients received more pre-treatment (oral contraceptive or 2-3 long-agonist doses) than those without (40,7% AD, 43,6% END vs 17,3% non-AD/END). Comparing patients with and without adenomyosis, no statistical differences were found in embryo transfer results between groups: clinical pregnancy rate (63% vs 56,9%), miscarriage rate (23,5% vs 14,1%), ectopic pregnancy rate (11,8% vs 4,7%) and live birth rate (40,7% vs 45,8%). No differences in gestational outcomes were observed in terms of the number of adenomyosis criteria present, the number of direct criteria, the type of criteria, or when differentiating between focal and diffuse adenomyosis. Similarly, there were no differences when comparing patients with both diagnoses to those with isolated adenomyosis. The most prevalent adenomyosis features reported were hyperechogenic islands (direct criteria), followed by an irregular junctional zone and asymmetrical wall thickening (indirect criteria). Finally, no differences were found in perinatal outcomes or complications during the pregnancy follow-up between groups. Limitations, reasons for caution Although this is the largest serie evaluating adenomyosisto the low adenomyosis prevalence in our population, these results should be confirmed in larger series. In our center all adenomyosis/endometriosis symptomatic patients are under medical treatment before assisted reproduction techniques, that may modify adenomyosis criteria over time and probably pregnancy outcomes. Wider implications of the findings This is the first study to characterize adenomyosis using the revised MUSA definitions in an oocyte donation programme. Applying these criteria and preparing endometrium with GnRH analog pretreatment and treating medically symptomatic patients before ART, adenomyosis did not adversely affect reproductive outcomes. Trial registration number Not applicable

O-213 Analysis of risk factors for monozygotic twins following in vitro fertilization-embryo transfer

Abstract Study question To investigate the risk factors associated with the incidence of monozygotic twinning（MZT）following in vitro fertilization and embryo transfer (IVF-ET). Summary answer MZT following IVF-ET may be associated with a reduced endometrial thickness on the day of embryo transfer and a decrease in estradiol levels post-transfer. What is known already MZT pregnancy arises from the division of a single fertilized ovum, resulting in offspring with identical genetic material. These twins exhibit markedly higher rates of complications compared to dizygotic counterparts, including increased incidences of miscarriage, congenital anomalies, intrauterine fetal demise, growth restriction, and preterm delivery. The underlying biological processes leading to MZT remain elusive. Presently, scholarly discourse centers around two predominant models and one hypothesis: the zygote division model, the embryonic membrane fusion model, and the over-mature gametes hypothesis, respectively. IVF-ET has been implicated in the heightened occurrence of MZT, suggesting a potential iatrogenic element to this phenomenon. Study design, size, duration A retrospective cohort study has been conducted. We analyzed 582 IVF-ET cycles at a large teaching hospital from January 2007 to December 2022, including 291 clinically confirmed MZTs, and 291 matched non-MZTs. Participants/materials, setting, methods A total of 582 participants, 291 in both MZT group and non-MZT group. There were 146 fresh embryo transfer cycles and 145 frozen-thawed cycles in the MZT group. Each cycle type was matched on a 1:1 basis by age and embryo transfer date with a control group that did not result in MZT following IVF-ET. We examined the disparities between the MZT group and the non-MZT group, and performed the Logistics regression analysis. Main results and the role of chance Significant differences were observed in the MZT group compared to the non-MZT group in the fresh embryo transfer cycle, particularly regarding estradiol (E2) and progesterone (P) levels on day 7 post-transfer, E2/P ratios on day 14 post-transfer, and endometrial thickness on the day of transfer (p<0.05). Logistic regression analysis indicated a correlation between reduced endometrial thickness on the transfer day and the occurrence of MZT. During the frozen-thawed cycle, significant differences were noted in E2/P ratios, E2 levels on day 7 post-transfer, and endometrial thickness on embryo transfer day (p<0.05). Logistic regression analysis suggested that lower E2 levels on day 7 post-transfer and reduced endometrial thickness on embryo transfer day were predictive of MZT. Additional potential influencing factors included the duration of the participants’ menstrual cycle, the protocol of ovulation induction, and the duration of embryo culture in vitro. Limitations, reasons for caution Primarily, the retrospective design may introduce bias, notably due to the potential absence of comprehensive data. Secondly, the study is constrained by the sample size, with 146 fresh cycles and 145 frozen cycles, which may not provide a fully representative statistical power. Wider implications of the findings The incidence of MZT may implicate signaling pathways at the maternal-fetal interface, with early embryonic split potentially serving as a compensatory mechanism in response to suboptimal estrogen levels or diminished endometrial thickness, thus enhancing embryonic viability. Trial registration number not applicable

P-027 Sperm motility and calcium ionophore treatment influence fertilization and pregnancy outcomes in TESE-ICSI

Abstract Study question Are there differences in fertilization and pregnancy rates post-TESE-ICSI between motile and immotile sperm, and do these vary in treatments with and without calcium ionophore? Summary answer Post-TESE-ICSI data reveals differences in fertilization and pregnancy rates when comparing motile vs. immotile sperm and treatments with and without calcium ionophore after TESE-ICSI. What is known already Testicular sperm extraction (TESE) followed by intracytoplasmic sperm injection (ICSI) poses a challenge for every IVF laboratory. This is particularly true in patients exhibiting azoospermia, where only a few and mostly immotile sperm are present in testicular tissue. In these cases, a calcium ionophore treatment for activation of the oocyte may help to overcome poor prognosis fertilization outcome, and thereby enhancing the likelihood to achieve a transfer leading to a successful pregnancy. Although both techniques, TESE-ICSI and activating substances are commonly applied, detailed analyses for individual counselling of couples are missing. Study design, size, duration This study analyzed 787 TESE-ICSI cycles (2015-2023) regarding patient age, number of attempts, oocyte maturity, fertilization and pregnancy rate after fresh embryo transfer. Cycles were split into four groups: (A) at least one motile sperm was injected (n = 493); (B) only immotile sperm were used (n = 294); (C) calcium ionophore (n = 474); (D) no calcium ionophore (n = 313). 17 cycles were excluded from the study because no sperm were found on the day of TESE-ICSI and oocytes were vitrified. Participants/materials, setting, methods In our IVF clinic, calcium ionophore treatments are only offered if a pre-screening of TESE samples reveals the absence of motile spermatozoa or if a previously conducted TESE-ICSI attempt resulted in a low fertilization rate (<30%) or a total fertilization failure. Statistical analyses was performed to compare the motile and immotile sperm group and the groups with or without calcium ionophore treatment. Main results and the role of chance No differences were found in all groups (A-D) regarding age of female or male patient and number of collected oocytes per group. However, our results demonstrate a difference in the mean number of ICSI attempts when comparing motile sperm and immotile sperm (2.0±1.3 vs. 2.3±1.6, p < 0.05), and when comparing attempts with calcium ionophore treatment and those without (2.4±1.6 vs. 1.8±1.8, p < 0.0005). The mean fertilization rate (2PN stage) was higher in the motile sperm group (A) compared to the immotile group (B) (57.8% vs. 28.4%, p < 0.0005) and also higher in attempts of group (D) in comparison to attempts of group C (56.8% vs. 40.2%, p < 0.0005). While fertilization failure occurred less often in group (A) (3.2%) it occurred to a higher rate in group (B) (19.4%), followed by group (C) (12.0%). Biochemical (BPR) and clinical pregnancy rates (CPR) showed a significant difference between the motile and immotile sperm group (BCR: 33.2% vs. 12.3%, p < 0.0005; CPR: 25.6% vs. 9.3%, p < 0.0005), but no differences between the two calcium ionophore groups. Limitations, reasons for caution This analysis was done retrospectively. A potential subgroup analysis of groups (A) and (B) into calcium ionophore use and of groups (C) and (D) into motile or immotile sperm will reveal the effect of calcium ionophore on success rates regardless of sperm motility. Wider implications of the findings Our data provides insight into success rates of TESE-ICSI cycles, especially if only immotile sperm were present. This will serve as a helpful guide for physicians when counseling patients about their success rates and to optimize the outcome in cases with poor prognosis by using a calcium ionophore treatment. Trial registration number not applicable

P-769 Congenital heart defects in children born after assisted reproductive technology: A large cohort study from the Committee of Nordic Assisted Reproductive Technology and Safety (CoNARTaS)

Abstract Study question Are children conceived after assisted reproductive technology (ART) more likely to be born with congenital heart defects (CHDs) than those born after spontaneous conception (SC)? Summary answer Major CHDs and severe CHDs are associated with ART, with a higher risk in both ART-conceived singletons and multiples compared to singletons from SC. What is known already Children born after ART have higher risk of birth defects compared to children born after SC. Among these defects, CHDs hold the highest prevalence, accounting for about 50% of all major birth defects and affecting approximately 1-2% of children in the general population. Several cohort studies and systematic reviews, among these a recent review including 41 studies and in total 25,856 ART children, shows increased risk of CHDs in children born after ART. However, conflicting findings have been reported for specific CHDs. Study design, size, duration This Nordic registry-based cohort study included 7,747,637 liveborn children, with 171,735 conceived after ART. All liveborn children (singletons and multiples) in Denmark (1994–2014), Finland (1990–2014), Norway (1984–2015), and Sweden (1987–2015) were included. National data from ART registries, medical birth registries, patient registries, cause of death registries, and population registries were cross-linked. Participants/materials, setting, methods The International Classification of Diseases (ICD) versions 8, 9, 10 were used for selection of CHDs. Major and severe CHDs were defined according to European Concerted Action on Congenital Anomalies and Twins (EUROCAT). Outcomes were major CHDs, severe CHDs, six hierarchical CHD lesion groups, and ten selected major CHDs. CHD diagnoses were considered prenatally or within the first year of life in Denmark, Finland, Sweden, and prenatally or at birth in Norway. Main results and the role of chance Major CHDs occurred among 1.84% (n = 3159) children born after ART and among 1.15% (n = 86,824) children born after SC, with adjusted odds ratio (AOR) 1.36; 95% CI 1.31–1.41. Risk was highest in multiples, regardless of conception method. Severe CHDs were detected in 0.35% (n = 594) children born after ART and in 0.26% (n = 19,375) children born after SC; AOR 1.30; 95% CI 1.20–1.42. When analysing the risk of CHD for the specific groups of CHDs by the hierarchical classification, children born after ART had higher risk of CHDs than children born after SC for five of the six lesion groups: conotruncal defects, non-conotruncal defects, ventricular septal defect, atrial septal defects, and other CHDs. ART was further associated with an elevated risk in four of ten selected major CHDs. Major CHDs occurred among 1.62% (n = 2059) singletons born after ART and among 1.11% (n = 18,539) singletons born after SC; AOR 1.19; 1.14–1.24. The prevalence of severe CHDs was 0.31% (n = 399) among singletons born after ART and 0.25% (n = 18,539) among singletons born after SC; AOR 1.20; 95% CI 1.09–1.33. In singletons born after ART, no difference was seen between ICSI and IVF or between frozen and fresh embryo transfer for major CHDs or severe CHDs. Limitations, reasons for caution A main limitation in this study is the lack of information on CHDs in miscarriages, pregnancy terminations, and stillbirths. Another limitation is that information on specific techniques used in assisted reproduction was not available from Finland. Lastly, we did not have information on causes of infertility. Wider implications of the findings CHDs, although rare, imply severe risks. Our study reveals an association between ART and major CHDs. While most CHD-affected children survive to adulthood, high morbidity and mortality rates persist in childhood and adulthood. The potential benefit of fetal echocardiography screening in ART pregnancies, beyond routine obstetric ultrasound, remains uncertain. Trial registration number ISRCTN 11780826

P-720 Ethnic diversity in fertility treatment in 2017-2021 using national register data, United Kingdom

Abstract Study question Are there any differences in fertility treatment use and outcomes across ethnic groups in the UK? Summary answer There are clear ethnic disparities – Black patients had lower IVF birth rates and started treatment later than White patients. What is known already Previous studies in US and UK have shown disparities in IVF outcomes, differences in perceptions around fertility treatment usage and prevalence of infertility across ethnicities. The mechanism in differences recorded in IVF outcomes by ethnicity is not fully understood due to the complexity influenced by existing social and economic inequalities, pre-existing diseases and other societal factors. Study design, size, duration The study used data from the UK national register held by the Human Fertilisation and Embryology Authority (HFEA), where all licensed clinics in the UK are required to submit treatment data. Participants/materials, setting, methods All treatment cycles recorded on the HFEA Register with a focus on cycles undertaken in 2017-2021 were analysed. This includes over 232,000 patients who had treatment between 2017 and 2021 and their partners. Five aggregated ethnic categories were used in most of the analyses (Asian, Black, Mixed, White and Other). Main results and the role of chance IVF pregnancy and birth rates have increased in all major ethnic groups since ethnicity data started being collected in 2008. However, Black and Asian patients consistently had lower pregnancy and birth rates compared with White patients. For Black patients aged 18-37, the average IVF birth rate per embryo transferred using fresh embryo transfers was on average 23%, compared to 32% for White patients in 2020-21. Among heterosexual couples, IVF cycles funded by the National Health Service (NHS) declined most among Black patients, decreasing from 60% in 2019 to 41% in 2021, compared to a decrease from 66% to 53% among White patients. Average age at starting treatment was higher among Black patients in heterosexual couples at 36.0 years of age, compared to the national average of 35.0 in 2021. Partner type varied by ethnicity and Black patients were more commonly single compared to other ethnic groups, with 6% of Black IVF patients and 62% of Black DI patients being single in 2017-21. Multiple birth rates have decreased across all ethnic groups, with disparities narrowing in recent years. Limitations, reasons for caution Due to the COVID-19 pandemic and large-scale work to upgrade the HFEA data submission system and migrate data to a new database, data on treatments and pregnancies from 2020-21 and outcomes from 2019-21 have not yet been validated. Around 13% of patients excluded due to unreported ethnicity data. Wider implications of the findings The HFEA and key stakeholders in UK have agreed a call to action to reduce the ethnic disparities through improving in development of clinical policy, information and awareness, NHS commissioning, and research to tackle the ethnic disparities in fertility treatment. Trial registration number NA

P-784 Visceral and subcutaneous adipose tissue in children born after assisted reproductive technology with frozen and fresh embryo transfer

Abstract Study question Is the distribution of abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) comparable between children following assisted reproduction and natural conception (NC)? Summary answer Children following frozen embryo transfer (FET) have significantly lower VAT/SAT-ratio than children following NC. However, this is not believed to be clinically important. What is known already It is well-established that an adverse distribution of the abdominal adipose tissue with high VAT/SAT-ratio increases the risk of cardiometabolic diseases, hence the VAT/SAT-ratio is closely related to the metabolic profile. Children conceived after FET and fresh embryo transfer (Fresh-ET) are at risk of being born large-for-gestational-age (LGA) and small-for-gestational-age (SGA), respectively. Both, being born LGA and SGA, increases the risk of obesity in later life. To the best of our knowledge, no studies have reported the VAT/SAT-ratio in children following assisted reproductive technology (ART) (both FET and Fresh-ET). Study design, size, duration Prospective observational cohort study including 150 singletons aged 7- to 10-years old conceived after FET (n = 50), Fresh-ET (n = 50) and NC (n = 50). All children were born in Eastern Denmark. The study is conducted between November 2018 and August 2020. Participants/materials, setting, methods This is a substudy af the “Health in Childhood following Assisted Reproductive Technology” (HiCART) study. The children underwent abdominal magnetic resonance imaging (MRI) for the quantification of abdominal adipose tissue along with measurements of anthropometric measurements, blood pressure, fasting blood samples and Dual-energy X-ray Absorptiometry (DXA) scan. The volumes of VAT and SAT were semi-automatically quantified blinded for the mode of conception. Multivariate linear regression analysis of the VAT/SAT-ratio was performed to adjust for confounders. Main results and the role of chance The VAT/SAT-ratio differed significantly between the three groups (mean SD; FET 0.26 (0.08), Fresh-ET 0.29 (0.07), NC 0.30 (0.08), ANOVA, p = 0.014). Pairwise comparison revealed that children conceived after FET had significantly lower VAT/SAT-ratio as compared to children conceived after NC (p = 0.007). In addition, children following FET tended to have lower VAT/SAT-ratio as compared to the Fresh-ET group (p = 0.059). Multivariate linear regression analysis of the VAT/SAT-ratio confirmed a lower VAT/SAT-ratio in FET after adjustment for potential confounding factors (child age and sex, maternal age at delivery and maternal BMI at pregnancy and child birth weight and BMI). Repeat-analysis of 20 MRI showed good intra-rater reliability of VAT and SAT quantifications. As previously reported in the HiCART studies, there were no differences between the groups in anthropometric measurements including body mass index (BMI), lean body mass, blood pressure or high-sensitivity C-reactive protein (hs-CRP). However, the level of triglycerides was found to be significantly higher in Fresh-ET compared to FET and NC (p = 0.028). Limitations, reasons for caution Selection bias cannot be excluded as only children from Eastern Denmark were invited. The observational nature of a cohort study prevents the establishment of causality. Wider implications of the findings Reassuringly, this study found no clinical important difference in abdominal adipose tissue between children following ART (both FET and Fresh-ET) and NC. However, future studies in larger cohorts are warranted. Trial registration number ClinicalTrials.gov identifier: NCT03719703

P-610 Elevated/high-normal TSH on day of beta-hCG in sub-clinical hypothyroid patients on levothyroxine associated with better odds of pregnancy in IVF cycles: a nested case-control study

Abstract Study question Is there an association between odds of achieving pregnancy and high-normal/elevated TSH levels in sub-clinical hypothyroid (SCH) patients on levothyroxine replacement who are undergoing IVF? Summary answer Odds of achieving pregnancy are significantly greater when TSH on day of beta-hCG is elevated/high-normal despite levothyroxine replacement in sub-clinical hypothyroid (SCH) patients undergoing IVF. What is known already TSH levels are known to increase following ovarian stimulation (OS). A 2023 Nature publication reported that in euthyroid patients undergoing fresh embryo transfer following OS and IVF, elevated/high-normal TSH levels (>2.5 mIU/mL) are associated with better pregnancy rates. Another recent study found no differences in IVF outcomes between SCH patients whose TSH was maintained=/< 4.2 mIU/mL on levothyroxine vs euthyroid controls. To the best of our knowledge, there are no prospective studies investigating possible association between pregnancy outcome and elevated TSH levels following OS within a cohort of SCH patients on levothyroxine replacement, using 2.5 mIU/mL as a strict cut-off. Study design, size, duration Nested case-control study performed between July-December 2023. PCOS and other endocrinopathies excluded. 100 SCH patients booked for fresh, blastocyst eSET cycles initially recruited after thyroxine replacement. 79 patients completed the study following 5 drop-outs and 16 cases of cycle cancellation/failure, cleavage-stage transfers and freeze-all. Odds of achieving pregnancy (‘cases’) in patients with elevated/high-normal TSH (‘exposure’) on day of beta-hCG determined by Odds Ratio, with beta-hCG negative patients serving as ‘controls’. First IVF cycle data analysed/presented. Participants/materials, setting, methods Study performed at an university-affiliated ART institute. Following institutional ethical clearance, patients with SCH (TSH>2.5 mIU/mL) recruited after informed consent. Levothyroxine replacement initiated to achieve TSH:0.5-2.5 mIU/mL and continued; followed by OS, antagonist IVF/ICSI cycles, hCG trigger and fresh blastocyst eSET. TSH measured again on day of beta-hCG (blinded). Odds Ratio calculated (IBM SPSS V.26) to determine odds of achieving pregnancy in high-normal/elevated group (TSH>2.5 mIU/mL) compared to low-normal group (TSH =/< 2.5 mIU/mL). Main results and the role of chance Baseline demographic characteristics of the single starting cohort of sub-clinical hypothyroid patients undergoing IVF/ICSI (n = 79) are summarized as mean±SD- age: 31.7±4.9 years, BMI: 27.9±14.2 kg/m2, AMH: 3.1±2.4 ng/mL, TSH before levothyroxine replacement: 5.5±2.7 mIU/mL. Data analysis showed that out of 63 patients in whom TSH level elevated > 2.5 mIU/mL on day of beta-hCG, 33 became pregnant (P.R- 52.4%); and out of 16 patients in whom TSH remained =/< 2.5 mIU/mL on day of beta-hCG, 3 became pregnant (P.R- 18.8%). Statistical analysis further revealed that odds of achieving pregnancy in elevated/high-normal TSH group was almost 5 times compared to odds of achieving pregnancy in low-normal TSH group (OR = 4.77, C.I= 1.24-18.37, at 95% confidence), considering TSH values on day of beta-hCG. Mean TSH in pregnant group (n = 36) was also found to be higher (4.2±1.6 mIU/mL) than mean TSH (3.9±1.9 mIU/mL) in those who did not get pregnant (n = 43). Limitations, reasons for caution Our study is limited by its modest sample size and adequately powered, larger prospective studies are needed before definite conclusions can be drawn from our data. Moreover, being an ongoing study, we do not yet have miscarriage and live-birth data for all patients and thus have not reported the same. Wider implications of the findings To our knowledge, this is the first prospective study documenting association between positive pregnancy outcome and high-normal TSH (using TSH>2.5 mIU/mL as cut-off) in SCH patients having fresh blastocyst eSET. Further investigation is required to determine if high-normal TSH following OS has protective impact on IVF, and its underlying mechanism. Trial registration number not applicable

O-303 What is the ideal dose of daily FSH after corifollitropin-alfa? A multicentre-randomized control trial

Abstract Study question Does the mean serum trigger-progesterone levels show significant variation based on the administered rFSH dose from day 8 onwards during ovarian stimulation using corifollitropin-alfa? Summary answer Lower rFSH doses from day 8 of ovarian stimulation onwards are linked to reduced serum progesterone (P4) levels without impact on cumulus-oocyte complexes. What is known already Progesterone elevation during ovulation trigger prompts a non-elective freeze-all strategy, given the lower live birth rates in fresh embryo transfers. Ongoing research explores methods to mitigate late follicular phase P4 rise to allow a fresh embryo transfer. Granulosa cells’ progesterone production is an FSH-driven and dose-dependent process, and FSH dose is furthermore pivotal for a good ovarian response. Balancing FSH dose is crucial for both optimal ovarian response and preventing undesirable P4 elevation while maintaining an adequate number of retrieved oocytes and allowing a fresh embryo transfer. Study design, size, duration This study is an interim-analysis of a randomized-controlled multi-center clinical-trial comparing three ovarian-stimulation-protocols: (A) corifollitropin alfa (CFA) followed by rFSH 50 IU/day; (B) CFA followed by rFSH 150 IU/day; (C) CFA followed by rFSH 250 IU/day.The primary outcome is the serum-progesterone-level on the day of hCG among the study groups, secondary outcomes included number of oocytes, clinical pregnancy rates and freeze-all cycles. 167 women (of 261) were randomized between July 2019-November 2023, with a 1:1allocation. Participants/materials, setting, methods Young (<40 years old), normo-ovulatory cycle (25-35 days), with AFC>7 and <20, and a BMI<29 Kg/m2 patients were recruited in the fertility clinic of three different tertiary university hospitals. On day 8 of ovarian stimulation (OS) following CFA administration, patients who needed additional rFSH were randomized into 3 groups (A-B-C). The OS was performed in a GnRH-antagonist protocol and the ovulation triggered with hCG. A fresh embryo-transfer was performed on day 5 following oocyte retrieval. Main results and the role of chance Overall, 167 patients were randomized, 60 in group A, 55 in group B and 52 in group C. The mean age and BMI were comparable between the groups. Mean AMH was respectively 2.2, 2.1 and 2.2 ng/mL, for group A, B and C (p = 0.95). Group A resulted in a significantly lower P4 level at trigger as compared with group B and C (respectively, 0.4ng/mL, 0.9 ng/mL and 1.4 ng/mL; p < 0.001). The mean number of retrieved oocytes was 10.7, 11 and 12.1 for group A, B and C, respectively (p = 0.47), while the mean number of mature oocytes was 7.3, 6.9 and 7.8 for group A, B and C, respectively (p = 0.7). A freeze-all approach was decided for 27%, 29% and 46% for group A, B and C respectively (p = 0.057). No significant differences were found for fresh-embryo-transfer outcomes (chemical pregnancy rates: 33%, 31% and 29%, respectively for A, B and C (p = 0.12).Of interest, comparisons between serum FSH at trigger showed a mean of 12.5, 17 and 20.5 IU/L for group A, B and C, respectively (p < 0.001) while the serum estradiol levels on day of trigger were comparable among the groups (1659, 2092 and 2098 ng/L for group A, B and C, respectively (p = 0.091). Limitations, reasons for caution This is an interim analysis planned to detect the mean difference in COC between groups. Therefore, the mean differences of the primary outcome should be interpreted as exploratory findings which warrant future investigation. Wider implications of the findings Administering a lower rFSH dose from day 8 onward during ovarian stimulation results in comparable numbers of COC but also leads to significantly lower serum P4 levels. Consequently, this finding has the potential to reduce the overall consumption of rFSH, thereby possibly increasing the likelihood of a fresh embryo transfer. Trial registration number NCT03686852