P-570 Determinants of reproductive outcomes following euploid blastocyst transfer: a retrospective cohort analysis
Abstract Study question Which clinical and biological factors contribute to the risk of pregnancy loss and the likelihood of live birth in pre-implantation genetic testing for aneuploidy (PGT-A)? Summary answer Adenomyosis and delayed embryo development significantly affect live birth rate (LBR) following euploid blastocyst transfer, while artificial endometrial preparation is associated with increased pregnancy loss. What is known already Embryo selection by PGT-A is intended to improve reproductive outcomes per transfer. While selecting euploid blastocysts does not improve cumulative LBR, PGT-A aims to reduce the time to pregnancy and lower the risk of pregnancy loss. However, despite genetic selection, many euploid embryos still fail to implant or result in non-viable pregnancies. Multiple factors, including maternal and paternal characteristics, as well as clinical and laboratory variables contribute to these outcomes. The relative importance of these factors may differ depending on the clinical indication for PGT-A. Study design, size, duration This retrospective cohort study includes patients who underwent frozen embryo transfer (FET) of a euploid embryo following intracytoplasmic sperm injection (ICSI) with trophectoderm biopsy (day 5/6) and PGT-A in a single tertiary university hospital between 2017 and 2023. Patients with additional testing for monogenic diseases or structural rearrangements were excluded. Participants/materials, setting, methods A total of 375 patients undergoing 533 FET cycles following PGT-A for specific clinical indications, including recurrent pregnancy loss (RPL), recurrent implantation failure (RIF) and advanced maternal age. Transfers were performed in either a natural (n = 248) or artificial cycle (n = 285). Cycle monitoring included serial hormonal and ultrasound assessments. Ultrasound-guided single embryo transfer was performed once endometrial thickness was deemed sufficient. Ovulation triggering and/or luteal phase support was prescribed at the discretion of the treating physician. Main results and the role of chance Following euploid blastocyst transfer, biochemical pregnancy rate was 69.0%, LBR was 51.2% and early pregnancy loss (EPL) rate was 18.5%. When considering only the first FET per patient (n = 375), biochemical pregnancy rate was 73.3%, LBR reached 56.3% and EPL rate was 17.3%. Univariate and multivariate analyses were conducted with GEE to adjust for multiple transfers per patient, with a sub-analysis performed on the first cycle of each patient. Multivariate logistic regression identified delayed embryo development, reflected in day 6 transfers, as significantly associated with lower LBR compared to day 5 (OR 0.55, 95%CI 0.34-0.90, p = 0.017). Additionally, the presence of adenomyosis was linked to reduced LBR (OR 0.42, 95% CI 0.22-0.79, p = 0.007). Importantly, the type of endometrial preparation (natural versus artificial) did not significantly influence LBR. Conversely, considering only first embryo transfer cycles, the rate of pregnancy loss per clinical pregnancy was significantly lower for natural cycle compared to artificial cycle FET (10% [11/114] vs. 24% [33/140]; p = 0.003, OR 2.3, 95% CI 1.3-4.2). A history of ≥ 2 pregnancy losses did not significantly influence live birth outcomes (p = 0.49), nor did we observe an association between LBR and the number of pregnancy losses when treated as a continuous variable. Limitations, reasons for caution The primary limitation is the retrospective design, which carries an inherent risk of bias. Patient heterogeneity and varying indications for PGT-A may have influenced both treatment decisions and success rates. Additionally, greater standardization in defining RIF and RPL would have enhanced data consistency. Wider implications of the findings Our findings highlight the impact of adenomyosis on live birth rates, emphasizing the need for subtype classification and refined treatment strategies. Additionally, the association between endometrial preparation and EPL provides clinicians with essential insights for optimizing FET management. Trial registration number No
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