The incidence, types and possible factors influencing mosaicism in human preimplantation IVF blastocysts. Analysis of results from a single IVF-PGT setting

Abstract Research question : Are there any intrinsic or extrinsic factors associated to embryo mosaicism incidence in IVF cycles? Design : This is a retrospective cohort study of PGT-A cycles performed at a university-affiliated IVF setting from October 2017 to October 2019. Trophectoderm biopsies were analyzed by Next Generation Sequencing (NGS). Mosaicism incidence, type of anomaly, and the chromosomes involved were analyzed. Intrinsic and extrinsic factors potentially inducing mosaicism were studied: maternal and paternal age, antral follicle count, cumulus-oocyte complexes retrieved, female body mass index, PGT-A indication, sperm concentration, total dosage of gonadotropins, embryo quality and day of blastocyst formation, single-step commercial media used, and biopsy operator. Results : The overall incidence of mosaicism in our PGT-A setting was 13.9%. In segmental mosaicism, larger chromosomes tended to be more affected, which was not observed regarding whole-chromosome mosaicism. Additionally, segmental mosaicism was mostly observed in monosomy (69.6%; p Conclusion(s) : Our results suggest remarkable differences in the mechanisms generating segmental and whole-chromosome mosaicism, indicating that they may deserve different consideration both when studying them and when prioritizing them for transfer. Male factor seems to be associated with mosaicism and may be worthy of specific assessment in future studies.