Embryo Blastomere Exclusion Identified in a Time-Lapse Culture System Is Associated with Embryo Ploidy

This study examined blastomere exclusion which is seen during embryo development and could represent imperfect cell division or a mechanism of aneuploidy correction. This was a retrospective cohort study which included embryos cultured in a time-lapse incubator undergoing preimplantation genetic testing for aneuploidy (PGT-A) with trophectoderm biopsy. Embryos were evaluated for blastomere exclusion early in development, late in development, both, or neither. Blastomere exclusion was compared to embryo ploidy. Embryos with no blastomere exclusion had an aneuploidy rate of 52.9%, while embryos displaying blastomere exclusion at any stage had an aneuploidy rate of 68.5% (p < .001). Early blastomere exclusion was not significantly associated with an increased aneuploidy risk (59.2% vs. 52.9% in no blastomere exclusions; p = 0.22). However, embryos with late blastomere exclusion were significantly more likely to be aneuploid, compared to embryos with no blastomere exclusions (77.5% vs. 52.9%; p < 0.001) as were embryos with both early + late blastomere exclusions (71.2% vs. 52.9%; p < 0.001). Upon restricting the analysis to aneuploid embryos, the presence of any blastomere exclusion was not significantly associated with complex aneuploidy, defined as 2 more affected chromosomes (43.9% vs. 38.7%; p = 0.28). However, the proportion with adverse embryo genetics significantly increased with the timing of blastomere exclusion (38.7%, 37%, 45.5%, and 50% for none, early, late, and early + late; p = 0.043). Late blastomere exclusion or a combination of both early + late blastomere exclusion was associated with an increased risk of aneuploid embryo genetics. Embryo selection using time-lapse culture systems should incorporate these findings when untested embryos are transferred.