Does human oocyte cryopreservation affect equally on embryo chromosome aneuploidy?

Oocytes cryopreservation as an important part of assisted reproductive technologies, which should ensure after warming not only intact oocyte morphological characteristics, but also their genetic apparatus stability. However, the meiotic spindle is very sensitive to the temperature fluctuations that can lead to unequal chromosome segregation during meiosis and as a consequence can cause embryo aneuploidy after oocyte fertilization. The aim of the study was to estimate the oocytes cryopreservation impact on human embryo chromosome aneuploidy. It has been shown that fertilization rate of the cryopreserved oocytes did not differ from fresh ones (83.1% vs 84% respectively). The number of blastocysts obtained from cryopreserved oocytes was less than that obtained from fresh oocytes, however, their morphological characteristics were better if compared the fresh oocytes. Our results showed different cryopreservation impact on aneuploidy rates of certain chromosomes in embryos obtained from cryopreserved oocytes. They had an increased aneuploidy of chromosome 13 and a decreased nondisjunction of chromosome 18 and sex chromosomes.

Embryological Characteristics and Preimplantation Genetic Testing for Aneuploidy of Embryos Derived from Cryopreserved Oocytes of Women of Different Reproductive Ages.

Oocyte vitrification is widely used for female fertility preservation. However, the efficacy of this procedure may depend on the women's age. The aim of the study was to compare the morphology, viability of cryopreserved oocytes, and their fertilization outcomes (fertilization, blastulation rate, level of embryo chromosomal aneuploidy-preimplantation genetic testing for aneuploidy [PGT-A]) in women of different reproductive ages. The studied oocytes were divided into groups depending on the age of patients: up to 30 years (group 1), 30-35 years (group 2), 36-40 years (group 3), and older than 40 years (group 4). It has been shown that in women of older reproductive age, the number of oocytes with polymorphism of endo- and extracytoplasmic structures was higher compared with younger patients. This could reflect on their cryosurvival rate, which was the highest in group 1 (98.1%) and the lowest was in group 4 (47.4%). With increasing age, the fertilization rate of cryopreserved oocytes and subsequent blastulation was decreased. However, the number of embryos with an aneuploid chromosome set number was increased. The chromosome set number euploidy rate of the embryos obtained from cryopreserved oocytes of advanced age women (group 4) did not differ from the fresh group with the same age (31.2% vs. 24.4%, p > 0.05), but the number of euploid embryos per patient was less than one (0.8 ± 0.1). Therefore, the decision to cryopreserve the oocytes of a patient of older reproductive age should be made individually for each situation, taking into account the prospects of obtaining full-fledged embryos and the chances of pregnancy.