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 565 mosaic embryos what key determinants influencing outcome? Summary answer Mosaic (diploid/aneuploid) have a significant developmental potential with good allowing personalized management evidence based prioritization for transfer. is known already Since first report healthy babies born after transfer, gradual accumulation knowledge on embryo transfers in International Registry Embryo Transfers provided necessary reassurance clinical embryos. Large comprehensive data from single centres consistent genetic counselling laboratory practices preimplantation prenatal testing offer valuable contribution to current practices. The aim this study was evaluate associations between aberrations, static morphology specific outcomes. design, size, duration This retrospective cohort that took place academic IVF centre (The CReATe Fertility Centre, Toronto, Canada), where we analysed results high resolution PGT-A, morphologic features 3529 frozen 2016-2022. Associated patient demographic data, outcome 2964 euploid were analyzed. Participants/materials, setting, methods All patients received prior High NGS PGT-A performed using Illumina platform BluGnome NxClinical analysis. Clinically relevant findings aberrations >10Mb mosaicism 25%-75%. Comparison morphological characteristics euploid, low-level (25%-<50% aneuploid cells trophectoderm biopsy), high-level mosaics (50% -75%) R-statistical package, Mathlab SSPS software. p < 0.05 CI 95% considered significant. Main role chance Of total transferred 77.1% had levels ≥25%-<50% (Group1-n=436): 54.8% segmental chromosome (SCM)gain/loss, 45.2% whole mosaicism(WCM)(trisomy/monosomy); 22.9% ≥ 50-<70% (Group2-n=129)(50.4% SCM 49.6% WCM). overall ongoing rate(OPR) 33% miscarriage rate 6%. Compared embryos, significantly lower implantation (p = 0,OD0.62-CI[0.5-0.7]) OPR(p 0,OD0.5-CI[0.4-0.6]). Pregnancy determined by level mosaicism: Group1 better implantation(p 0.005,OD1.8-CI[1.18-2.78]) OPR compared Group2. independently affected SCM(p 0.003) WCM(p 0.02) WCM rates 0.005,OD1.6-CI[1.15-2.27]). monosomies lowest impanation all (14% 8%,respectively). Within Group2 associated higher Birth available 118 mosaic-FET 802 euploid-FET. There no difference birth weight No gross-fetal anomalies reported group at birth. one termination<20GW due fetal stillbirth. For transfers, 11 anomalies, there 7-terminations 2-stillbirths. Limitations, reasons caution Although largest date evaluated genomic, numbers still low analyze impact chromosomal outcome. Wider implications should be prioritized mosaicism, type aberration morphology. than however established pregnancies result term normal weight. Trial registration number Canada