The lack of generally accepted indications for preimplantation genetic testing (PGT) and the inconsistency of the results of IVF procedures with and without testing make it necessary to analyze more deeply the features of early human embryogenesis and the reasons for the high level of chromosomal abnormalities in preimplantation embryos (PE). Proposed to prevent the transfer of defective embryos into the uterus of couples, carriers of monogenic and other genetic pathologies, preimplantation genetic diagnostics has become increasingly used in the future, especially with the beginning of restrictions on the number of embryos transferred to the uterus, to choose the best ones for transfer. In the article, the author substantiates his own point of view on the reasons for the high level of genetic disorders in PE as the ability of human embryos inherited in evolution, on the one hand, to a high level of plasticity and mutation, and on the other, to self — correction in the process of development. This should be taken into account when deciding on indications for PGT, evaluating the results of testing and deciding on the transfer of an embryo to the uterus. This also dictates the need for maximum information of patients about the methods of PGT, the peculiarities of the biology of the trophectoderm and embryoblast, the ability of embryos to self-correction, as well as the role of PGT and prenatal genetic diagnosis in preventing the birth of a sick child.