P-747 Chromosomal mosaic characteristics among women under IVF treatment: multicentric study of 2282 mosaic embryos diagnosed by preimplantation genetic testing with trophectoderm biopsy

Abstract Study question Which chromosomal mosaic features do women under IVF treatment show? Summary answer Single aneuploidies were the most represented among mosaic embryos and their frequency as well as the level of mosaicism increased in older women. What is known already Chromosomal mosaic embryos are characterised by the presence of chromosomally different cell lines within the same embryo. We previously demonstrated that reproductive potential of mosaic embryos is affected by the complexity of and the number of aneuploid cells present in trophectoderm (TE) biopsy. Although with the introduction of next generation sequencing (NGS) chromosomal constitution of human embryos have been elucidated, only limited number of mosaic have been characterised. Therefore, we performed a larger-scale multicenter study on mosaic embryos to examine the patterns and prevalence of chromosome specific mosaicisms in TE samples. Study design, size, duration This is a retrospective cohort study from May 2019 to May 2021 of 20200 embryos obtained from 5770 women under IVF treatment. From this cohort, 2280 mosaic embryos were analysed. All embryos were cultured to blastocyst stage; TE biopsy was performed on Day-5 of development or on Day-6/7 for slow growing embryos. Participants/materials, setting, methods TE biopsies underwent comprehensive chromosome screening (CCS) utilizing validated NGS. TE biopsies were classified as mosaic if they had 20%-80% of abnormal cells. For statistical analysis, embryos were divided in: single whole-chromosome trisomy, double whole-chromosome trisomies, single whole-chromosome monosomy, double whole-chromosome monosomies and complex aneuploidy (more than two different aneuploidies) groups. In addition, the frequency of single, double and complex segmental aneuploidies was evaluated. For each group, the trend related to maternal age was examined. Main results and the role of chance Among 2282 mosaic embryos single (whole-chromosome and segmental) aneuploidies were the most represented(52%) followed by complex(36%) and double ones(14%). When embryos were divided based on different types of aneuploidies, complex aneuploidies were the most frequent(34%) followed by segmental(31%), single monosomies(14%), single trisomy(12%). The more affected chromosomes within trisomies were 16(7%), 19 (7%), 21 and 22(6%). Monosomy involved mainly chromosomes 7(8%), 21 and 22(7%). Chromosomes 1, 5(9%), and 9(8%) were the most targeted by segmental duplication w