Introduction: Aneuploidy is one genetic factor leading to the failure of embryo implantation. At present, the collection of embryo cells for PGT is carried out according to the speed of embryo development on either the 5th or 6th day of blastulation. This study aimed to investigate the relationship between the day of embryo blastulation and the ploidy status of embryo, to select embryos with the most likelihood of being euploid in a noninvasive way.
Methods: This retrospective study recruited women undergoing preimplantation genetic testing (PGT) for aneuploidy with trophectoderm biopsy, first ovarian stimulation cycles only. First Faculty of Medicine and General Teaching Hospital patients were included in the retrospective study in cycles with PGT (83 PGT A, 28 PGT M, 14 PGT - SR). Embryos were cultivated 5-6 days, average age of patients was 37 years. For biopsy we used good quality blastocyst with good expansion of blastocele cavity and the integrity of both the inner cell mass and trophectoderm cells. Just embryos of A type: EB 4AA, 4AB,4BA,5AA,5AB,5BA,6AA,6AB,6BA [1] and embryos of B type: EB 4BB, 3AB,3BB [1] were PGT evaluated.
Results: 250 blastocysts from PGT cycles were evaluated. The euploid rate (number of euploid embryos divided by sum of all PGT tested embryos) of day 5 A-blastocysts was significantly higher than that of day 6 A blastocysts, either from the first ovarian stimulation cycles only: 39% (46/119) vs 28% (16/57) . In the case of B blastocysts the effect was even stronger : euploid rate of day 5 B embryos was higher than that of day 6 : 29% (8/28) vs 13% (6/46), either from the first ovarian stimulation cycles. The euploid rate of day 5 was higher than that of day 6 blastocysts, either from the first ovarian stimulation cycles only: 35% (62/176) vs 28% (14/74). The euploid rate of A blastocysts was higher than that of B blastocysts: 37% (54/147) vs 21% (22/103).
Conclusion(s): The euploid rate of A-blastocysts was significantly higher than that of B blastocysts. This effect was stronger for 6 th day blastocysts. So, if we for any reason apply non PGT cycles it can be hepful to determine the categories of blastocysts (A, B), so that on the 5th and especially the 6th day, we can select a significantly more suitable embryo (A) for transfer.
This work was supported by project of the First Faculty of Medicine and General Teaching Hospital