O-196 Evidence-based management of mosaic embryos - a single Centre experience from prospective transfer and birth outcomes of 565 mosaic embryos

Abstract Study question What are the pregnancy and neonatal outcomes of prospective transfer of 565 mosaic embryos and what are the key determinants influencing the outcome? Summary answer Mosaic (diploid/aneuploid) embryos have a significant developmental potential with good neonatal outcomes allowing personalized management and evidence based prioritization of embryos for transfer. What is known already Since the first report of healthy babies born after mosaic transfer, the gradual accumulation of knowledge on mosaic embryo transfers in the International Registry of Mosaic Embryo Transfers provided the necessary reassurance for clinical management of mosaic embryos. Large and comprehensive data from single centres with consistent clinical genetic counselling and laboratory practices for preimplantation and prenatal testing offer valuable contribution to the current practices. The aim of this study was to evaluate the pregnancy and neonatal outcomes after mosaic embryo transfers and to evaluate for associations between embryo genetic aberrations, static morphology and specific outcomes. Study design, size, duration This is a retrospective cohort study that took place in a single academic IVF centre (The CReATe Fertility Centre, Toronto, Canada), where we analysed the results from high resolution PGT-A, embryo morphologic features and pregnancy outcomes of 3529 frozen embryo transfers from 2016-2022. Associated patient demographic data, transfer outcome and neonatal outcome of 2964 euploid and 565 mosaic embryo transfers were analyzed. Participants/materials, setting, methods All patients received genetic counselling prior to frozen embryo transfer. High resolution NGS PGT-A was performed using the Illumina platform and BluGnome and NxClinical for data analysis. Clinically relevant findings were aberrations >10Mb and mosaicism from 25%-75%. Comparison of clinical and morphological characteristics of euploid, low-level mosaic (25%-