Freshet Research Articles

Trace elements exposure affects the outcomes of in vitro fertilization embryo transfer, a cohort study in Northern China.

With urbanization and industrialization process accelerated, humans are exposed more and more trace elements. This study aimed to explore the potential associations of trace elements with the outcomes of in vitro fertilization embryo transfer (IVF-ET). Total 181 women who underwent IVF-ET were enrolled, among which 89 women underwent fresh ET after IVF. Trace elements were measured in the serum and follicular fluid (FF) samples by inductively coupled plasma-mass spectroscopy. The associations of the levels of different trace elements with IVF-ET outcomes, including normal fertilization, high-quality embryos, and clinical pregnancy (fresh ET) were analyzed. Twenty-five out of twenty-eight trace elements showed higher concentrations in the serum than those in the FF. Normal fertilization was positively associated with Cu and Mn in the FF. High-quality embryos was positively associated with Cu in the serum and FF, and Zn in the serum. Clinical pregnancy was positively associated with Ge in the serum, and inversely associated with Al, Ba, and Pb in the serum. Additionally, poor outcomes of IVF-ET should be noticed in women with FF level of Cu < 955.38ng/mL, FF level of Mn < 3.42ng/mL, serum level of Ge < 6.11ng/mL, serum level of Al > 28.44ng/mL, and serum level of Pb > 0.90ng/mL. IVF-ET outcomes were positively associated with Cu, Mn, Zn, and Ge, and inversely associated with Al and Pb. Properly controlling the exposure of relevant trace elements is necessary for patients with the need of IVF-ET.

Non-genetic risk factors for preeclampsia: an updated umbrella review

Abstract Background Preeclampsia (PE) is a common pregnancy disorder with complex mechanisms, and multiple risk factors may contribute to its development. Our objective is to update our literature search from our previous umbrella review, summarizing recent evidence on non-genetic risk factors associated with PE and assessing their credibility to identify those supported by robust epidemiological evidence. Methods We searched PubMed, EMBASE, Scopus, and ISI Web of Science up to June 2023. For each meta-analysis, we computed summary effect estimates, 95% confidence intervals, 95% prediction intervals, and assessed heterogeneity using I², while also examining small-study effects and excess significance bias. Quality assessment was conducted using the AMSTAR-2 tool. Results 89 meta-analyses were identified, providing data on 219 associations. Of these, 151 (69%) showed statistically significant findings at P &amp;lt; 0.05, with 52 (24%) remaining significant at P &amp;lt; 10-6. Large or very large heterogeneity was observed in 121 (55%) associations. Evidence for small-study effects and excess significance bias was found in 27 (12%) and 29 (13%) associations, respectively. Only 16 (7%) presented convincing evidence: Polycystic Ovary Syndrome (PCOS), PCOS (adjusted), Obstructive Sleep Apnea (OSA), Obesity (adjusted), Chronic Kidney Disease (CKD), Pregnancy Intrahepatic Cholestasis, SARS-CoV-2 infection (adjusted), Oocyte donation (OD) vs. In vitro fertilization (IVF), Fresh embryo transfer vs. spontaneous conception (SC) (singleton), Frozen embryo transfer vs. SC, OD vs. SC (singleton), IVF-OD vs. IVF-AO, IVF-OD fresh ET vs. IVF-AO fresh ET, NC frozen embryo transfer vs. AC frozen embryo transfer, Fetal sex (term), and Smoking. Conclusions Maternal health conditions like PCOS, along with reproductive interventions such as OD and IVF, as well as lifestyle factors like obesity and smoking, showed convincing associations with PE. Key messages • Maternal health conditions, reproductive interventions, and lifestyle factors showed compelling evidence of association with preeclampsia. • Our findings emphasize the multifactorial nature of preeclampsia and suggest potential avenues for further research and clinical intervention.

Legal framework and IVF outcomes: a comparative analysis of fresh and frozen embryo transfers in Switzerland

Research question: To what extent do legislative measures impact standard reproductive outcome parameters? Design: Retrospective cohort study using data from the Swiss national IVF registry analysing the outcomes of 13908 women undergoing ETs resulting from their first lifetime oocyte retrieval before (2014-2016) or after (2020-2022) the revised legislation, allowing extended culture for 12 zygotes. Live birth rates (LBR) and cumulative LBR (cLBR) were compared in fresh and frozen ET strategies in both periods. Adjusted multivariable mixed model analyses were performed to determine odds ratios (OR) and incidence rate ratios (IRR). ResultsBefore the revised legislation, LBR was higher in fresh compared to frozen ET (27.2% vs. 22.7%). After the revised legislation, LBR was lower in fresh ET (29.3% vs. 36.3%) and cLBR was higher in freeze-all strategy (cLBR: 59.0% vs. 39.8%). However, in a multivariable analysis, fresh and frozen ETs did not differ in the odds of live birth (OR = 1.08, 95% CI: 0.95-1.22) and freeze-all were not found to be more effective than fresh strategies (IRR = 1.12, 95% CI 0.98 - 1.27). In a subgroup analysis, fresh blastocyst ET showed higher LBR than cleavage stage ET (OR = 2.01, 95% CI 1.62-2.49). ConclusionThe change in national legislation provided the unique opportunity to evaluate the legal impact on reproductive outcomes: Besides a reduction of multiple deliveries, LBR of frozen ET improved, resulting in a comparable success of fresh and frozen transfer strategies. In addition to technological improvement, the legal framework influences the evolution of clinical practice, thereby contributing to enhanced reproductive outcomes.

The impact of blastocyst grade on singleton birth weight in fresh IVF‒ET cycles in ART: a retrospective study

BackgroundThe positive correlation between embryo quality and pregnancy outcomes has been confirmed in many studies, but there are few on the impact of embryo quality on neonatal weight, especially among neonates from fresh IVF‒ET cycles in ART. Therefore, this study aimed to compare the birth weights of infants from different blastocyst grades in fresh IVF-ET cycles and explore related factors affecting birth weight.MethodsThe main outcome measure was singleton birth weight. A total of 1301 fresh cycles of single blastocyst transplantation and single live birth profiles were retrospectively analyzed and divided into four groups according to blastocyst quality: the excellent group (grade AA), which included 170 cycles; the good group (grade AB/BA), which included 312 cycles; the average group (grade BB/CA/AC), which included 559 cycles; and the poor group (grade BC/CB), which included 260 cycles. The relationships among cystic cavity expansion, endocytic cell mass, ectodermal trophoblast cell grade, and birth weight were studied. Multiple linear regression analysis was performed to investigate the relationship between blastocyst quality and neonatal birth weight and logistic regression for the risk factors for low birth weight newborns.ResultsWith decreases in the blastocyst quality, including ICM, TE quality, and embryo expansion stage, birth weight declined, and Z scores correspondingly decreased. After adjusting for confounders, the average and poor groups (P = 0.01 and P = 0.001, respectively) and blastocysts with TE grade C (P = 0.022) resulted in singletons with lower birth weight. Additionally, the poor group and blastocysts with Grade C TEs had a greater chance of leading to low birth weight infants compared with the other groups.ConclusionOur findings indicated that excellent and good-grade blastocyst transplantation could achieve better pregnancy outcomes and that average and poor-grade blastocyst transplantation, especially with grade C TEs, were associated with single birth weight loss. No association was found between the embryo expansion stage or ICM quality and neonatal birth weight.

Incidence and timing of pregnancy loss following timed artificial insemination or timed embryo transfer with a fresh or frozen in vitro-produced embryo

The aim of this study was to characterize the incidence and timing of pregnancy loss from service event (timed artificial insemination or timed embryo transfer) to parturition. Lactating Holstein-Friesian cows were randomly assigned to receive either artificial insemination (AI, n = 243) or embryo transfer (ET, n = 863) with a fresh or frozen in vitro-produced blastocyst derived from oocytes collected from the ovaries of elite dairy donors (n = 14 Holstein Friesian and n = 8 Jersey) and elite beef donors (n = 21 Angus) using transvaginal ovum pick-up. In addition, oocytes were collected from the ovaries of beef heifers of known pedigree following slaughter at a commercial abattoir (n = 119). Blood samples were collected on d 7 from all cows to determine progesterone concentration and from subsets of cows on d 18 (n = 524) and d 25 (n = 378) to determine mRNA abundance of interferon-stimulated gene-15 and pregnancy-specific protein B concentration, respectively, to provide an early pregnancy diagnosis. Transrectal ultrasonography was conducted to determine pregnancy status on d 32, d 62 and d 125 after synchronized ovulation. Parturition date was recorded for all cows that reached a term delivery. The predicted probability of pregnancy (%) varied at each time point (d7, 18, 25, 32, 62, 125, parturition) depending on treatment (AI: 77.0, 60.2, 52.3, 48.8, 47.0, 44.6, 44.0; fresh ET: 100.0, 69.5, 60.3, 56.1, 48.4, 46.8, 45.5; frozen ET: 100.0, 61.7, 52.2, 41.6, 32.9, 31.8, 30.2). Irrespective of treatment, the largest proportion of pregnancy loss occurred in the period from service event (AI on d 0 or ET on d 7) to d 18, with minimal loss occurring between d 62 and parturition (AI: 1.8%, fresh ET: 1.9%, frozen ET: 3.5%). Treatment differences in the predicted probability of pregnancy per service event were detected between fresh ET vs frozen ET on d 32 and both AI and fresh ET vs frozen ET on d 62, 125 and at parturition. There was greater probability of pregnancy loss between d 32 and 62 following ET (Fresh: 11.3%, Frozen: 18.0%) than AI (4.0%). The percentage of cows that calved following transfer of a fresh embryo (45.5%) was similar to AI (44.0%), but less when a frozen embryo was transferred (30.2%). In conclusion, AI and fresh ET led to a greater probability of a cow becoming pregnant and maintaining the pregnancy to term than frozen ET. Cows that were still pregnant on d 62 had a very strong likelihood of maintaining the pregnancy to full-term parturition, irrespective of treatment. Further work is required to improve the likelihood of pregnancy establishment and reduce embryonic and fetal mortality following transfer of a cryopreserved in vitro-produced embryo.

In vitro fertilization results of GNRH antagonists and medroxyprogesterone acetate used to prevent premature LH surge during ovarian hyperstimulation

The aim of this study was to evaluate the effects of medroxyprogesterone acetate (MPA) treatment in comparison to those of gonadotropin releasing hormone (GnRH) antagonists for the prevention of premature luteinizing hormone surges during controlled ovarian hyperstimulation (OS) and the impact of these effects on developing embryos and pregnancy outcomes. Data from 757 cycles of GnRH antagonist treatment and 756 cycles of MPA treatment were evaluated at the Akdeniz University Faculty of Medicine Assisted Reproductive Treatment Center between October 2018 and April 2022. Patient records were obtained from the electronic database of the centre and analysed. In our centre, GnRH antagonist protocols were used between 2018 and 2020, and MPA protocols were used between 2020 and 2022. We chose our study population by year. Our study is a comparative retrospective study. All methods in this study were performed in accordance with the relevant guidelines and regulations. Patients using MPA were significantly older (33.9 ± 5.6 vs. 32.6 ± 5.6, p < 0.001) and had a lower number of antral follicles (AFC) (10.7 ± 8.6 vs. 11.9 ± 10.8, p = 0.007) than those using GnRH antagonists. Both MPA (2.9%) and GnRH antagonists (2.2%) had similar effectiveness in preventing premature ovulation (p = 0.415). There was no significant difference between the two groups in terms of the number of total developed embryos (1.3 ± 1.3 vs. 1.2 ± 1.2, p = 0.765). There was no significant difference in the clinical pregnancy rates with the first ET (%35.4 vs. %30.1, p = 0.074), per total number of transfers (35.3% vs. 30.1%, p = 0.077). MPA was found to be effective at preventing premature ovulation during OS treatment, and the incidence of developing embryo and pregnancy outcomes in patients using MPA were similar to those in patients using GnRH antagonists. Therefore, the use of MPA instead of GnRH antagonists during OS may be a viable alternative for patients not scheduled for fresh ET.

O-290 Reduced uterine artery pulsatility index (UtAPI) in artificial frozen embryo transfer pregnancies leads to underestimation of 1st-trimester preeclampsia risk. An analysis of over 30,000 pregnancies

Abstract Study question Does the mode of conception (spontaneous, ovulation induction, fresh or frozen embryo transfer) impact Uterine Artery Pulsatility Index (UtAPI) values in 1st-trimester preeclampsia screening? Summary answer A significant reduction in UtAPI during 1st-trimester screening is observed in artificial frozen embryo transfer (AC-FET) pregnancies, resulting in underestimated preeclampsia risk. What is known already Accumulating evidence indicates that AC-FET cycles are associated with an increased risk of preeclampsia. Uterine artery (UtA) Doppler is a crucial biomarker for first-trimester preeclampsia screening, along with maternal factors and serum biomarkers, identifying “high-risk” patients. Guidelines strongly recommend the administration of aspirin(150mg/day) in these women, owing to robust evidence demonstrating a 40% reduction in the incidence of preeclampsia. Despite small studies suggesting a lower UtAPI after frozen ET, no previous studies explored the impact of the type of endometrial preparation in UtAPI Doppler or its influence on estimating preeclampsia risk Study design, size, duration This is a retrospective single-center study including 33880 singleton pregnancies (spontaneous or after ART) who underwent the 1st-trimester ultrasound screening at our University Hospital between January 2010 - May 2023. Overall, 33880 pregnancies were included: 29709 spontaneous, 429 ovulation induction, 1015 fresh ET and 2727 after frozen ET pregnancies (326/2727 in NC-FET and 2401 in AC-FET). Participants/materials, setting, methods The study included only singleton pregnancy for which a first trimester ultrasound (11+0- 13+6 wks) with UtA Doppler was performed. The primary aim of the study was to assess whether there was an association between the mode of conception and the UtA Doppler and whether UtAPI differed according to the type the endometrial preparation for FET. Continuous variables were expressed as mean ± SD. ANOVA test and multivariate regression analysis were performed. Main results and the role of chance Overall, the 1st-trimester UtAPI in pregnancies conceived after AC-FET was 1,036±0,160 [CI95%:0,723;1,349], after NC-FET 1,354±0,162 [CI95%:1,037;1,671], Fresh-ET 1,418 ±0,161 [CI95%:1,104;1,733], OI 1,413±0,162 [CI95%:1,096;1,730] and spontaneous pregnancies 1,373 ± 0,160 [CI95%:1,060;1,686]. A multivariable regression analysis, adjusting for confounding factors (age, weight, smoking, and oocyte donation), demonstrated that the value of uterine artery UtAPI is significantly lower when artificial cycle for frozen embryo transfer is performed compared with spontaneous pregnancies (-0,337 ± 0,014 [CI95%:-0,378;-0,297]), ovulation induction (-0,377 ± 0,028 [CI95%:-0,455; -0,298]) Fresh-ET (-0,383 ±0,021 [CI95%:-0,442; -0,323]), and NC-FET (-0,318 ± 0,029[CI95%:-0,401; -0,23]). On the contrary none of the other modes of conception are different in terms of UtAPI as compared with spontaneous pregnancies. Among screened patients, the number of patients classified at high risk for preeclampsia was significantly lower in pregnancies following AC-FET 7.8%(156/2002) as compared to NC-FET 15.9%(46/289), fresh-ET 11.0%(58/527), ovulation induction 10.5%(26/248) and spontaneous pregnancies (1452/15624) p &amp;lt; 0.001. Nonetheless, despite the lower number of high-risk patients in the AC-FET group, the actual incidence of PE was more than three times higher in AC-FET group 5.2%(125/2401) as compared with spontaneous 1.5%(431/29709), ovulation induction 1.4%(6/429) or NC-FET pregnancies 1.5%(5/326) and more than two times higher when compared to fresh-ET pregnancies 2.3%(23/1015) p &amp;lt; 0.001. Limitations, reasons for caution Despite employing a robust methodology with a substantial sample size and multivariate statistical analysis to address confounding factors, it’s essential to acknowledge the possibility of residual bias. However, its impact on the presented outcomes is anticipated to be minimal. Wider implications of the findings Existing 1st-trimester preeclampsia screening calculators overlook the notably lower UtAPI in AC-FET pregnancies, as discovered in our study. This poses a threat of underestimating high-risk patients and neglecting prophylactic aspirin. Algorithms should be adjusted to accurately assess risk for those undergoing AC-FET Trial registration number Not applicable

O-320 Does applying an ‘elective freeze-all’ policy work in practice? A matched cohort study of over 9,000 embryo transfers

Abstract Study question Does application of a Freeze All Embryo (FAE) policy achieve superior live birth rates in practice compared to fresh IVF transfer cycles? Summary answer FAE FETs achieved significantly higher LBRs than fresh for both the first ET per cycle and cumulatively per cycle. What is known already The efficacy of vitrification methods has led to segmentation between the ovarian stimulation and embryo transfer cycle becoming increasingly applied. Randomised controlled trials have shown that for high responders, especially those at risk of ovarian hyperstimulation syndrome, the FAE approach is likely to be favourable. However, whether a routine freeze all approach applied in routine clinical practice improves outcomes in a broader group of patients remains unclear. Study design, size, duration This is a retrospective analysis of 7,647 autologous fresh oocyte retrievals and 9,609 subsequent ETs, performed between 2016-2022. The primary study aim was to compare (cumulative) live birth rates between fresh and frozen thawed embryo transfers after FAE IVF cycles. The groups consisted of 3,707 fresh IVF transfers plus 1,533 subsequent FETs derived from those cycles, versus 3940 FAE cycles with 3969 subsequent FETs. Participants/materials, setting, methods 5,808 patients underwent fresh oocyte retrievals (2016-2022) at a single UK-based centre. In total, 4,997 of these patients underwent 9,609 ETs; either fresh or frozen. For analysis, FAE cycles and fresh IVF cycles underwent 1:1 full propensity score matching for age and number of eggs collected, using probit regression of treatments on covariates. Logistic regression analyses were fit including full matching weights in the estimation to compare LBR superiority between groups. Main results and the role of chance Patients undergoing fresh transfers were significantly older and yielded significantly fewer oocytes per retrieval (37 and 36, P &amp;lt; 0.001; 7 ± SE 0.07 and 12 ± SE 0.1, P &amp;lt; 0.001, respectively). After full 1:1 matching for age and oocytes collected, the means for both groups were 36 and 15, respectively. Standardised mean differences after matching was &amp;lt;0.2. The first FET from FAE cycles achieved significantly superior LBRs and was a significant predictor of LB compared to fresh ETs when adjusted for covariates (37% and 26%, respectively, aOR 1.3; 95% CI 1.2-1.5, P &amp;lt; 0.001). Cumulative LBs achieved per cycle were also significantly higher for FAE cycles (56% and 37%, respectively). When stratifying by age, first ET LBRs between groups were comparable for &amp;lt;35s (FAE 42%, fresh 40%). However, with increasing age, FAE first FETs achieved higher live births than fresh transfers (35-37, 36% and 33%; 38-39, 34% and 23%; 40-42, 27% and 14%; 43-45, 15% and 5%, respectively). Limitations, reasons for caution This is a retrospective analysis and, although cohorts underwent full 1:1 matching, inherent bias may be present within the data and must be considered when drawing conclusions. Wider implications of the findings These findings suggest that in clinical practice, FETs after a FAE cycle may achieve superior LBRs compared to fresh ETs, particularly in older patients and for higher responders. Overall, FAE cycles were observed to result in higher cumulative LBRs per cycle than cycles that begin with a fresh transfer. Trial registration number Not applicable

O-076 Novel method to enhance preantral follicle growth by granulocyte colony-stimulating factor administration improves embryos and pregnancy rate in poor ovarian reserve: a randomized controlled trial

Abstract Study question Whether priming with granulocyte colony-stimulating factor (G-CSF) before ART improves embryo and pregnancy rate while increasing anti-Müllerian hormone (AMH) in patients with poor ovarian reserve. Summary answer G-CSF priming improved embryonic development and pregnancy rate in ART with poor ovarian reserve, simultaneously increasing serum AMH. Enhanced preantral follicle growth likely was responsible. What is known already Eleven years ago, we treated repeated implantation failure in 10 women with diminished ovarian reserve by administering G-CSF with embryo transfers. No implantation succeeded directly, but serendipitously 3 of the 10 spontaneously became pregnant 2 months later. One of these pregnancies involved twins in a 45-year-old woman without ovulation induction. We hypothesized that G-CSF administration might have stimulated preantral follicle growth, with improved ovulation after 2 months. In animal models with diminished ovarian reserve, G-CSF administration consistently increased ovarian preantral follicles and AMH. Therefore, we designed this clinical trial. Study design, size, duration Patients were prospectively randomized to priming or control groups. All patients initially underwent conventional infertility treatment for 2 consecutive cycles in which the priming group but not controls received a subcutaneous G-CSF priming injection during the early luteal phase. Each group then underwent 1 cycle of IVF/ICSI and fresh embryo transfer (IVF/ICSI-fresh ET), followed by cryopreserved ET if needed until live birth or embryo depletion. AMH was measured before and after priming. Participants/materials, setting, methods Hundred ART patients 20 to 42 years old with AMH below 2 ng/mL were randomized to priming or control groups (50 patients each). None had over 1 ART failure, day-3 follicle-stimulating hormone (FSH) above 30 IU/L, uterine anomalies, or a partner with azoospermia. Main results and the role of chance Fertilization rate, embryonic development, and implantation rate by fresh ET were significantly improved by G-CSF priming. Clinical and ongoing pregnancy rates by IVF/ICSI-fresh ET were significantly higher with priming (30% and 26% in 47 ART patients; 3 delivered with conventional treatment) than in controls (12% and 10% in 49 ART patients; 1 dropped out). With priming, significantly more patients achieved cryopreservation of redundant blastocysts (53% with priming vs. 24% in controls). The cumulative live birth rate was 32% in 50 patients with priming, significantly higher than 14% in 49 controls (relative risk, 2.8; 95% confidence interval, 1.04-7.7). Infants derived from priming had no congenital anomalies, while infant weights, birth weeks, and Apgar scores were similar between groups. Among 4 variables (age, day-3 FSH, AMH, and priming), logistic regression significantly associated age and priming with cumulative live birth. Priming significantly increased serum AMH. The efficacy of G-CSF priming was not associated with genotypes for killer-cell immunoglobulin-like receptors. No adverse effects of priming were observed. Limitations, reasons for caution Enhancement of preantral follicle growth by G-CSF administration needs to be confirmed histologically as this clinical trial could not allow ovarian biopsies for its purpose of infertility treatments. Wider implications of the findings This study proposes a novel, simple, and safe treatment for poor ovarian reserve. In addition, enhancement of preantral follicle growth by G-CSF priming may also improve ovulatory dysfunctions in polycystic ovary syndrome with elevated AMH, reflecting pooling of retarded/arrested growing preantral follicles. Trial registration number UMIN000013956

P-679 The impact of polycystic ovary syndrome (PCOS) on placental pathology among singleton livebirths conceived following in-vitro fertilization (IVF) or ovulation induction/intrauterine insemination (OI/IUI) treatments

Abstract Study question Are there differences in placenta pathology between PCOS and non-PCOS infertility diagnosis among singleton livebirths conceived following either IVF or OI/IUI treatments? Summary answer PCOS diagnosis when compared to non-PCOS exhibits distinctive associations within the anatomic and vascular spectrum of placental pathology. What is known already Pregnancies of women with PCOS are at higher risk for maternal and neonatal morbidity. Available studies suggest a possible association of PCOS with hypoxia-induced placental findings among natural conceptions, and a possible role of chronic, low-grade inflammation on decidualization, trophoblast invasion, and placental vascularization. Given the high prevalence of PCOS among women seeking fertility treatments there is significant interest in human placental research. Nevertheless, the impact of PCOS on placental pathology among singleton livebirths conceived with fertility treatments remains unclear. Study design, size, duration Retrospective review of data from 1398 singleton livebirths with available placenta pathology. All pregnancies were conceived following fertility treatments (IVF:1004, OI/IUI: 394) at an academic fertility center and were delivered at the same hospital between 01/2004 and 04/2022. 1196 patients had an infertility diagnosis other than PCOS (uterine factor excluded) and 193 had been diagnosed with PCOS (based on Rotterdam criteria). Placenta pathology (classified as below) was compared between PCOS and non-PCOS patients. Participants/materials, setting, methods Placental findings were reviewed by one expert pathologist and classified further as anatomic, inflammatory, infectious, and vascular [including any features of fetal(FVM) or maternal(MVM) vascular malperfusion], using the Amsterdam Workshop Consensus definitions. Primary outcomes: anatomic, inflammatory, infectious, and vascular. Parametric/non-parametric tests were used as appropriate. Adjusted odds ratios(adjOR) with 95% confidence intervals (95%CI) were calculated utilizing logistic regression, controlling for potential confounders. Subanalyses were performed separating IVF from OI/IUI-conceptions, and fresh from frozen embryo transfers(FET). Main results and the role of chance PCOS compared to non-PCOS patients were younger, with higher BMI and AMH [mean (SD): 32.9(3.5) vs 35.1(3.8) years, p &amp;lt; 0.001; 26.1(5.5) vs 24.8(5.5)kg/m2, p = 0.003; 9.1(5.8) vs 3.5(3.4)ng/ml, p &amp;lt; 0.001, respectively]. Overall, neither unadjusted rates (35.2% vs 28.8%, p:0.072; 15.9% vs 11.8%, p = 0.115; 21.8% vs 20.0%, p = 0.568; 51.0% vs 57.3%, p = 0.103, PCOS vs. non-PCOS, respectively), nor adjOR (95%CI) [1.02(0.94-1.1), 1.01(0.95-1.08), 1.02(0.94-1.09), 0.96(0.88-1.05), non-PCOS: ref] showed any differences between groups in anatomic, inflammatory, infectious, and vascular abnormalities, respectively. When separating IVF from OI/IUI-conceptions, and fresh transfers from FETs, adjOR(95%CI) revealed no differences between groups in anatomic, inflammatory, and infectious abnormalities [OI/IUI: 1.01(0.87-1.16), 1.0(0.88-1.13), 1.0(0.88-1.13); Fresh ET: 1.01(0.9-1.14), 1.02(0.95-1.1), and 0.95(0.85-1.05); FET: 1.16(0.96-1.4), 1.0(0.87-1.16), and 1.11(0.93-1.33), for anatomic, inflammatory, and infectious abnormalities, respectively, non-PCOS: ref]. Interestingly, a lower rate of vascular abnormalities was noted among PCOS patients in OI/IUI [adjOR(95%CI): 0.83(0.73-0.96)], but not among fresh or FET cycles [adjOR(95%CI): 1.05(0.91-1.19), and 0.97(0.8-1.18), respectively]. In FET cycles, within vascular abnormalities, lower rates of high grade FVM among PCOS patients were noted [adjOR(95%CI): 0.96(0.93-0.99)]. Furthermore, and although anatomic abnormalities did not differ between groups, a lower incidence of single umbilical artery [adjOR(95%CI): 0.98(0.96-0.99)] was noted among PCOS patients in IVF cycles. Limitations, reasons for caution The study is limited by its retrospective design and focuses on an infertile population undergoing treatments, limiting generalizability. Comparisons with PCOS patients conceiving naturally may provide meaningful insights. Variability among PCOS phenotypes, and other environmental, and lifestyle factors might also alter a patient’s individual pregnancy risk for placental abnormalities. Wider implications of the findings PCOS may impact placental pathology in a distinct way, within the anatomic and vascular spectrum, which might differ from that of other infertility causes and might be further altered by the treatment protocol. Our study adds to the limited human placental research specific to pregnancy of women with PCOS. Trial registration number Not Applicable

O-039 Con - the faster the better

Abstract Late o’clock: Are slow growing embryos clinically usable? Con - the faster the better Reproductive medicine and, within it, embryology, have experienced milestones in the understanding of pre-implantation embryonic development over the last quarter of a century. The development of blastocyst culture media for embryo culture even after embryonic genome activation and the possibility of continuous monitoring of embryonic morphokinetics throughout the pre-implantation period have been major contributors. The development of molecular genetic techniques has also played an important role. The introduction of new cryopreservation techniques has also improved the success rate of the clinical use of surplus embryos, including slow-growing embryos not otherwise selected for fresh cycle transfer. Two questions are most frequently encountered in clinical embryology today: which embryo in a cohort has the best chance of resulting in a live-born child, and how slow and morphologically suboptimal can an embryo be to still be considered clinically useful? In particular, the latter question does not have an easy answer, as embryos demonstrate varying pace of development. A further problem arises if there are no optimal embryos available in the cohort and this answer has to be given on day 2, 3 or 5, as this is when the embryo transfer is scheduled to take place. Some studies suggest that longer timing of any stage of embryonic development from pronuclear fading onwards means that the embryo is late in development due to certain abnormalities and is likely to be energetically depleted by the activation of its repair mechanisms. Such embryos not only have a lower implantation potential compared to fast embryos, but also diverge in time from the optimal receptivity of the endometrium. Additional testing and/or storage of slow-growing embryos brings the question of their clinical usability to the time of frozen embryo replacement cycles and quiets the couple's expectation of a “successful” completion of the stimulated cycle. Whether embryos are to be selected for fresh ET or FER, the “the faster - the better” principle is likely to be applied. In daily clinical practice, decisions on the use of slow-growing and/or morphologically sub-optimal embryos and the timing of embryo transfer are made on an individual basis, taking into account various medical as well as non-medical (e.g. economic, logistical) factors. These may also include portraying a positive image of the centre's performance. However, patients expect infertility specialists to make realistic assessments not only of the viability of slow growing embryos, but also of the outcome of the transfer of them. The assessment must be based not only on medical and ethical but also on rational grounds.

P-026 Retrospective descriptive analysis of 1300 ICSI-AOA cycles: evaluating clinical outcomes and child health in the context of artificial oocyte activation (AOA)

Abstract Study question How does the outcomes of ICSI-AOA and child health differ from those reported in the literature? Summary answer ICSI-AOA clinical outcomes, including fertilization, embryo quality, pregnancy, live birth rates, and anomaly rates in children, align with those reported for ICSI alone. What is known already The use of AOA to artificially induce calcium rises by employing calcium ionophores has been shown as an effective approach in overcoming fertilization failure following ICSI, especially in couples facing severe male factor infertility. However, a significant gap exists in reporting live birth outcomes. On the other hand, uncertainties surrounding the health implications for children born through this method necessitate further investigation due to the limited sample sizes in previous reports. This descriptive analysis fills that gap by assessing 1300 cases, providing crucial insights into the clinical outcomes and health status of babies resulting from ICSI-AOA treatment. Study design, size, duration This retrospective study analyzes 1300 cases of ICSI-AOA between 2018 and 2020. Clinical outcomes in this study includes: fertilization, embryo quality, pregnancy, and live birth rates. Questionaries regarding the children health were included from birth to two years. Participants/materials, setting, methods The study included 1300 cases that referred to Isfahan Fertility and Infertility Center (Isfahan, Iran) and underwent ICSI-AOA due to: 1) cases with testicular biopsy (N = 458), 2) cases with 99-100% sperm head abnormal morphology and/or 3) previous low fertilization or total fertilization failure after ICSI (N = 842). In all cases, to induce AOA, oocytes were subjected to a 10-minute exposure of 10 micromolar ionomycin following ICSI. Main results and the role of chance From 1300 couples, 11,756 mature, 2,012 immatures, 193 degenerate, and 76 uninjectable oocytes were obtained. Fertilization were 59.69%, and 52.18% for mature and immature oocytes, resulting in cleavage rates of 96.93% and 93.80%, respectively. On day 3, 25.14% grade A, 31.49% grade B, and 43.36% grade C were observed. In 321 couples, 571 fresh embryos were transferred on day 3, resulting in clinical pregnancy and live birth rates of 20.82%, and 19.55%, respectively. For 32 couples with 44 fresh ET on day 5, rates were 9.38%, and 9.38% respectively. Out of 3270 vitrified embryos on day 3, 1743 were thawed (337 couples) and 1147 were transferred in 643 ET cycles. Clinical pregnancy and live birth rates were 21.61%, and 20.37%, respectively. 1527 embryos remain frozen. Out of 2,974 day 5-embryos, 2,571 did not reach blastocyst, leaving 403 vitrified embryos in 699 cases. Among them, 197 embryos remain frozen (80 cases) while 206 were transferred, with clinical pregnancy and live birth rates of 22.11%, and 21.80%, respectively. Cancellation rate, encompassing failed fertilization, cancellations on multiple days, and after freeze-thawing, was 20.16%. Among 266 live births, seven children showed anomalies, including achondroplasia, combined immunodeficiency, left eye deviation, intrauterine growth restriction, hydrocephaly, epilepsy, and umbilical hernia. Limitations, reasons for caution The main limitations of this study were the lack of comprehensive information on previous cycles, the absence of an ICSI control group, and the limited long-term follow-up on the physical and mental health of children born through the ICSI-AOA method beyond age two. Wider implications of the findings ICSI-AOA yields helpful clinical outcomes in high fertilization, pregnancy, and live birth rates in infertile couples, especially those with severe male factor infertility similar to ICSI in literature. Furthermore, presently, there seem to be no real concerns about health of babies born through this method, aligning with ICSI studies. Trial registration number IR.ACECR.ROYAN.REC.1401.038

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-706 The pregnancy rates in a large cohort of patients with thin endometrium when stratified according to estradiol levels on the day of triggering

Abstract Study question Is there any difference in ongoing pregnancy rate in women with thin endometrium (&amp;lt;8 mm) when scrutinized based on estradiol levels on triggering day? Summary answer Either with a low, moderate, or high estradiol level on the day of triggering, ongoing pregnancy rates do not change in patients with thin endometrium. What is known already Endometrial thickness has been argued to be one of the proxy determinants of endometrial receptivity. In that context, although the optimal thickness has been widely stated to be between 8-14 mm, the negative effect of thin endometrium on pregnancy outcome is still controversial in in-vitro-fertilization (IVF) cycles. Nevertheless, particularly lack of large sample size of women with thin endometrium among the available literature, is the leading factors that avoids to solid conclusion.Furthermore, it might be hypothesized that patients with thin endometrium and accompanying low estradiol might be distinct from women with thin endometrium despite relatively high estradiol level. 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. Only patients having an endometrial thickness &amp;lt;8 mm on the day of triggering were recruited. Other inclusion criteria was having at least one blastocyst to be transferred. All frozen-thawed embryo transfer cycles were excluded. Female age and body mass index were not considered as an exclusion criterion. Participants/materials, setting, methods During the study period, a total of 3076 IVF cycles with fresh ET were employed. Of them, 814 had an endometrial thickness of &amp;lt; 8 mm on the day of triggering. Among 814 IVF cycles, 25th, 50th and 75th quartiles of estradiol levels on the day of triggering referred to 322.8, 755.7 and 1310.5 pg/ml, respectively. The number of IVF-ET cycles in the 1st, 2nd, 3th and 4th quartiles were 203, 204, 204 and 203. Main results and the role of chance The mean (SD) age of women recruited in the final analyses was 36.5 (5.5) years and endometrial thickness was 7.2 (0.8) mm. The pregnancy rates per ET with regard to 1st, 2nd, 3th and 4th quartiles were 37.6%, 33.0%, 37.3% and 44.3%, respectively without any statistical significance (p = 0.134). However, the respective ongoing pregnancy rates were 26.1%, 18.1%, 22.1%, 31.0 % and the highest quartile had a statistically superior ongoing pregnancy rates than the second (p = 0.003) and third quartiles (p = 0.022). When binary logistic regression analysis was performed by inserting the female age, body-mass index, duration of infertility and quartiles of estradiol levels on the day of triggering, only female age remained as an independent factor for the prediction of an ongoing pregnancy (RR: 0.92 CI95%: 0.87 to 0.98, p = 0.008). Utilization of estradiol level as a continuous variable in the same model also failed to present the independent validity of it to predict an ongoing pregnancy. Notably, the lowest thickness of a positive pregnancy resulting with an ongoing pregnancy was 4.7 mm. Limitations, reasons for caution The inherent risks cannot be excluded due to the retrospective nature of the current study, which had been efforted to overcome with regression analysis. Wider implications of the findings The current study includes one of the largest numbers of experience particularly with thin endometrium on the day of triggering. However, having a thin endometrium despite low or relatively high estradiol level does yield any prediction for the pregnancy outcome. Trial registration number Not Applicable

Current understanding of the pathogenesis of placenta accreta spectrum disorder with focus on mitochondrial function.

The refinement of assisted reproductive technology, including the development of cryopreservation techniques (vitrification) and ovarian stimulation protocols, makes frozen embryo transfer (FET) an alternative to fresh ET and has contributed to the success of assisted reproductive technology. Compared with fresh ET cycles, FET cycles were associated with better in vitro fertilization outcomes; however, the occurrence of pregnancy-induced hypertension, preeclampsia, and placenta accreta spectrum (PAS) was higher in FET cycles. PAS has been increasing steadily in incidence as a life-threatening condition along with cesarean rates worldwide. In this review, we summarize the current understanding of the pathogenesis of PAS and discuss future research directions. A literature search was performed in the PubMed and Google Scholar databases. Risk factors associated with PAS incidence include a primary defect of the decidua basalis or scar dehiscence, aberrant vascular remodeling, and abnormally invasive trophoblasts, or a combination thereof. Freezing, thawing, and hormone replacement manipulations have been shown to affect multiple cellular pathways, including cell proliferation, invasion, epithelial-to-mesenchymal transition (EMT), and mitochondrial function. Molecules involved in abnormal migration and EMT of extravillous trophoblast cells are beginning to be identified in PAS placentas. Many of these molecules were also found to be involved in mitochondrial biogenesis and dynamics. The etiology of PAS may be a multifactorial genesis with intrinsic predisposition (e.g., placental abnormalities) and certain environmental factors (e.g., defective decidua) as triggers for its development. A distinctive feature of this review is its focus on the potential factors linking mitochondrial function to PAS development.

What is the Optimum Endometrium Needed for Implantation?

Implantation most critical step in reproduction. A complex process where blastocyst becomes intimately connected with maternal endometrium/decidua and requires; Competent embryo at blastocyst stage Receptive endometrium Synchronized dialogue between maternal and embryonic tissues Endometrial Changes for Implantation include architectural, morphological, cytochemical, molecular and genetic. These Changes Induce Endometrial receptivity, which is endometrial lining in a state of readiness for blastocyst implantation. It involves acquisition of adhesion ligands and loss of inhibitory components that may act as a barrier to an attaching embryo. Receptive endometrium is capable of selecting good quality embryos and reject the incompetent embryos. Endometrial Evaluation includes 1. Non-Invasive Assessment of Endometrial Receptivity by USG 2. Detection of abnormal Uterine cavity by 3D USG/SIS, HSG and Hysteroscopy 3. Diagnose Chronic Endometritis by hysteroscopy and Molecular tests? 4. Endometrial Microbiome by molecular tests 5. Endometrial asynchrony - Proteomics and transcriptomics 2D and 3D Ultrasound can Identify patients with poor implantation prognosis but has low predictive value in determining endometrial receptivity and IVF outcome. Ideal endometrial thickness for optimal outcome is between 7-14 mm. No Association was seen between clinical pregnancy rates (CPR) and endometrial pattern for women undergoing in IVF with fresh ET and FET. Minimum Endometrial Volume associated with pregnancy is 1.59 mL – 3D. But most pregnancies occur in volumes of 2-13 mL. Evaluation of endometrial volume is particularly useful in synechiae, adenomyosis and uterine anomalies. Vascularity demonstrated within Zone 3 or within Zones 3 and 4 prior to transfer is associated with good implantation rate. Presence of &gt;3 peristaltic contractions of the sub endometrial myometrium/2 minutes interval on Day of hCG administration associated with poor implantation. Diagnosis of chronic endometritis is based on hysteroscopy, endometrial biopsy with plasma cells being identified histologically and specific treatment is determined based on microbial culture. Existence of non-Lactobacillus bacteria in the endometrium is correlated with negative impacts on reproductive function and should be considered as an emerging cause of implantation failure and pregnancy loss. Endometrial Receptivity Array (ERA) is validated for analysing the expression of 238 genes that are intimately related to endometrial receptivity. Abnormality in endometrial receptivity is displayed a specific gene expression profile. Intrauterine secretory profile directly linked to successful implantation and evaluation of endometrial fluid for cytokine, interleukin and growth factor secretions can be used to assess the endometrium. Conclusion: Identification of one or more of endometrial parameters that definitely indicate receptivity for implantation remains an elusive goal. None of the endometrial receptivity markers have sufficient discriminatory value to act as a diagnostic test for endometrial receptivity based on their ability to predict clinical pregnancy. Due to the dynamic, cyclic nature of the endometrium it may be difficult, to reliably assess endometrial function on the basis of a single test.

Risk factors associated with monozygotic twinning in offspring conceived by assisted reproductive technology.

What are the factors influencing the occurrence of monozygotic (MZ) twins in offspring conceived by assisted reproductive technology (ART)? Parental ages, the transfer of fresh versus frozen embryos, and the grade of blastocysts are all related to MZ twinning in ART offspring. Offspring conceived by ART have significantly increased risk of MZ twins, which may be due to the characteristics of the infertile population. The objective of this study was to explore the incidence of monozygotic (MZ) twins after ART and to clarify the risk factors for MZ twinning. A total of 255 monozygotic twins were enrolled in this cohort study, and then matched with singletons at a ratio of 1:4 randomly (with 1020 in the control group). All offspring were conceived by single embryo transfer. The collected data were divided into the following three aspects for analysis: characteristics of the infertile population, gamete or embryo manipulations, and factors related to embryo development. The incidence of MZ twins was 1.638% (255 out of 15 567 pregnancies after single embryo transfers). Compared to singleton births, a significantly lower rate of frozen embryo transfers (FET; 78.0% vs 86.1% P = 0.002) was seen amongst the MZ twins. Amongst fresh ETs, the rate of blastocyst transfers in the MZ twins group was higher compared to that in the control group (92.9% vs 75.4%, P = 0.005). We also found that certain grades of blastocysts in terms of trophectoderm (TE) development, inner cell mass + TE development and the classification of 'top-quality' embryos were associated with the incidence of MZ twinning (P = 0.025, P = 0.012, P = 0.020, respectively). Logistic regression analysis revealed that higher paternal age (odds ratio (OR) = 0.94, 95% CI = 0.89-1.00, P = 0.029) and FET (OR = 0.48, 95% CI = 0.33-0.68, P = 0.001) may be protective factors against MZ twinning. However, higher maternal age (OR = 1.07, 95% CI = 1.01-1.13, P = 0.027) and the transfer of blastocysts (OR = 4.31, 95% CI = 1.46-12.73, P = 0.008) appeared to be associated with an increased risk of MZ twinning. Amongst blastocyst transfers, a C grade TE may be protective factor against MZ twinning (B: OR = 1.90, 95% CI = 1.18-3.07, P = 0.009; A: OR = 1.58, 95% CI = 0.93-2.67, P = 0.089). First, our definition of MZ twins was based on twins' birth after single embryo transfers (SET), rather than ultrasound examination during early pregnancy. Second, the parental characteristics of the two groups were homogenous, so it was difficult to find any associations between infertility factors and the incidence of MZ twins. This multifaceted analysis of the risk factors for MZ twinning provides some information for clinical interventions in high-risk populations. This study was supported by the National Key Technology Research and Developmental Program of China (2022YFC2704404), CAMS Innovation Fund for Medical Sciences (2021-I2M-5-001), Taishan Scholars Program for Young Experts of Shandong Province (tsqn201909195), the Basic Science Center Program (31988101), and the Shandong Provincial Key Research and Development Program (2020ZLYS02). All authors have no conflicts of interest to declare. N/A.

Cluster analysis reveals a homogeneous subgroup of PCOS women with metabolic disturbance associated with adverse reproductive outcomes.

Polycystic ovarian syndrome (PCOS) is a heterogeneous and complex reproductive endocrinological disease that could lead to infertility. There were many attempts to classify PCOS but it remains unclear whether there is a specific subgroup of PCOS that is associated with the best or worst reproductive outcomes of assisted reproductive techniques (ART). Infertile PCOS patients who underwent their first cycle of in vitro fertilization (IVF) in West China Second University Hospital, Sichuan University from January 2019 to December 2021 were included. Basic clinical and laboratory information of each individual were extracted. Unsupervised cluster analysis was performed. Controlled ovarian stimulation parameters and reproductive outcomes were collected and compared between the different clusters of PCOS. Our analysis clustered women with PCOS into "reproductive", "metabolic", and "balanced" clusters based on nine traits. Reproductive group was characterized by high levels of testosterone (T), sex hormone-binding globulin (SHBG), follicular stimulation hormone (FSH), luteinizing hormone (LH), and anti-Müllerian hormone (AMH). Metabolic group was characterized by high levels of body mass index (BMI), fasting insulin, and fasting glucose. Balanced group was characterized by low levels of the aforementioned reproductive and metabolic parameters, except for SHBG. Compared with PCOS patients in reproductive and balanced clusters, those in metabolic cluster had lower rates of good quality day 3 embryo and blastocyst formation. Moreover, PCOS patients in the reproductive cluster had greater fresh embryo transfer (ET) cancelation rate and clinical pregnancy rate after fresh ET than metabolic cluster (odds ratio [OR] = 3.37, 95% confidence interval [CI]: 1.77-6.44, and OR = 6.19, 95% CI: 1.58-24.24, respectively). And compared with PCOS of metabolic cluster, PCOS of balanced cluster also had higher chance for fresh ET cancelation (OR = 2.83, 95% CI: 1.26-6.35). Our study suggested that PCOS patients in metabolic cluster may be associated with adverse reproductive outcomes and might need individualized treatment and careful monitoring before and during ART.

Effect of blastocyst morphology on the incidence of monozygotic twinning pregnancy after single blastocyst transfer

Aims: To explore whether blastocyst morphology [blastocyst stage, inner cell mass (ICM), and trophectoderm (TE) grading] impacts the occurrence of monozygotic twinning (MZT) after single blastocyst transfer (SBT).Materials and methods: A single-center retrospective cohort study was conducted including all clinical pregnancies after single blastocyst transfer between January 2015 and September 2021 (n = 9229). Blastocyst morphology was assessed using Gardner grading system. MZT was defined as more than one gestational sac (GS), or two or more fetal heartbeats in a single GS via ultrasound at 5–6 gestational weeks.Results: The overall MZT rate was 2.46% (227 of 9229 cases), of which was the highest in blastocysts of grade A TE and lowest in those with grade C TE (grade A: B:C = 3.40%:2.67%:1.58%, p = .002). Higher risk of MZT pregnancy was associated with higher trophectoderm grading [A vs. C: aOR, 1.883, 95% CI 1.069–3.315, p = .028; B vs C: aOR, 1.559, 95% CI 1.066–2.279, p = .022], but not extended culture in vitro (day 5 vs. day 6), vitrification (fresh vs. frozen-thawed ET), assisted hatching (AH), blastocyst stage (stage 1–6) or ICM grading (A vs. B).Conclusions: We conclude that TE grade is an independent risk factor of MZT after single blastocyst transfer. Blastocysts with high-grade trophectoderm are more liable to obtain monozygotic multiple gestation.

P-256 Large for gestational age in singletons born following frozen embryo transfer: due to freezing technique or to endometrial preparation protocol? Lessons from the French registry

Abstract Study question Is large for gestational age (LGA) observed in singletons born following frozen embryo transfers (FET) either due to freezing technique or to endometrial preparation protocol? Summary answer Artificial cycles were associated with a higher rate of LGA when compared to ovulatory cycles, whereas no difference was observed between the freezing techniques. What is known already Several studies compared neonatal outcomes after fresh embryo transfer (fresh ET) and FET, and showed that FET was associated with improved neonatal outcomes, including reduced risks of preterm birth, low birth weight and small for gestational age (SGA) when compared to fresh ET. However, these studies also revealed an increased risk of LGA after FET. The underlying pathophysiology remains unclear; parental infertility, laboratory procedures including embryo culture conditions and freezing-thawing processes, as well as endometrial preparation treatments might be at play. Study design, size, duration A multicentric epidemiological data study was performed through a retrospective analysis of the standardized individual clinical records of the French national registry of in vitro fertilisation (IVF) from 2014 to 2018, including deliveries resulting from fresh ET and FET that were prospectively collected in fertility centres. Complementary data were collected from the participating fertility centres including the vitrification media and devices, as well as the endometrial preparation protocols. Participants/materials, setting, methods Data were collected from 35 French fertility centres, leading to the inclusion of a total of 72,789 fresh ET, 10,602 slow-freezing FET and 30,062 vitrification FET cycles. Fetal growth disorders were defined in liveborn singletons according to gestational age and sex-specific weight percentile distribution: SGA and LGA if &amp;lt; 10th and &amp;gt;90th percentile, respectively. Analyses were performed using linear mixed models with the centres as random effect. Main results and the role of chance Among a total of 26,585 liveborn singletons, 16,413 babies were born from fresh ET, 1,644 from slow-freezing FET and 8,528 from vitrification FET. Birthweight was significantly higher in the FET groups compared to the fresh ET group, with no difference between the two freezing techniques. Likewise, LGA rates were higher and SGA rates were lower in the FET groups compared to the fresh ET group (12.0% vs 6.4%, p &amp;lt; 0.001, and 7.8% vs 13.4%, p &amp;lt; 0.001 respectively). In a multivariable analysis, the risk of LGA following FET was not different between stimulated and natural cycles (adjusted odds ratio: 1.06, 95% confidence interval: 0.83-1.35, p = 0.64) but was significantly increased in artificial compared to natural cycles (aOR 1.36 [1.11-1.67], p = 0.003). On the contrary, the risk of LGA was not associated with either the freezing mode (slow-freezing vs vitrification) or the embryo stage (cleaved embryo vs blastocyst). When focusing on vitrification, the risk of LGA was not associated with either the freezing medium used or the embryo stage, and no difference was observed according to the vitrification device. Limitations, reasons for caution Most of the vitrification techniques were performed using the same device, and with two major vitrification media, limiting the interpretability of the comparison of the risk for LGA according to the device or the vitrification media. Wider implications of the findings Our results seem reassuring regarding potential fetal growth disorders following embryo vitrification in comparison to slow-freezing. Even if other factors may be involved, the impact of the endometrial preparation treatments seems to prevail for LGA risk following FET. FET during ovulatory cycles could minimize the risk for fetal growth disorders. Trial registration number N/A