Late embryo cleavage as an indicator of chromosome aneuploidy by pre-implantation genetic screening

During in vitro fertilization (IVF), not all patients receive good quality oocytes or embryos. This study investigated the frequency of aneuploidy and mosaicism in embryos obtained from parthenogenetic oocytes and poor morphological embryos that also exhibited late cleavage development by preimplantation genetic screening (PGS). Twenty late cleavage embryos under IVF treatment were cultured until day 5, and one of the blastomeres was biopsied. The embryos were divided into three groups (parthenogenetic oocytes and poor-quality embryos with dark cytoplasm, several vacuoles or fragments in the cytoplasm; arrested embryos; and good-quality embryos). All samples were tested for abnormalities using array-comparative genomic hybridization (a-CGH). Twenty late cleavage-stage embryos were biopsied and analyzed for aneuploidy. A total 17 of 20 (85%) embryos were aneuploid and three (15%) were euploid. The incidence of aneuploidy in good-quality embryos was 75%, while poor-quality embryos displayed a higher frequency (86.7%) of aneuploidy. The parthenogenetic oocytes were invariably aneuploid (100%). Based on the embryo-grading system by Veeck, embryo grades 1 and 2 exhibited a lower incidence of aneuploidy (75%), while grades 3 and 4 showed 1.33-times higher aneuploidy rates (RR = 1.33; p < 0.001). The numerical defects of the chromosomes increased with the percent of fragmentation, with fragmented embryos showing 1.32-times greater aneuploidy rates than the non-fragmented ones. Embryos with uneven blastomeres showed 1.07-times higher aneuploidy rate when compared with embryos showing even blastomeres (p < 0.0064). Late embryo cleavage results in a higher incidence of aneuploidy and mosaicism upon comparison with early embryo cleavage.