Chromosomal abnormalities originate predominantly from female meiosis, so the direct analysis of the outcome of the first and second meiotic divisions allows performing preimplantation genetic testing for aneuploidy (PGT-A). This approach to PGT-A revealed novel information on the prevalence of meiotic errors and significantly different chromosomal profile from those described in previous meiotic studies, allowing a high accuracy of the oocyte genotype prediction in pre-selection of embryos resulting from aneuploidy-free oocytes. Although, this is no longer a standard PGT-A practice, its utilization is still the only choice in the population settings, where embryo manipulation is not allowed. It also provides a unique information on the origin and mechanism of human chromosomal abnormalities detected in the current PGT-A based on NGS and blastocyst biopsy. It is particularly essential in distinguishing meiosis or mitosis origin of the resulting embryo mosaicism in pre-selection and prioritization of transfer of such embryos, to ensure the highest potential for pregnancy and birth of a healthy offspring.