Embryonic ploidy correction: an update on mechanisms and insights from mosaic embryo transfer

Preimplantation human embryos frequently exhibit aneuploidy and chromosomal mosaicism, yet emerging evidence suggests they may possess mechanisms for ploidy correction that can mitigate these abnormalities. Several potential pathways have been proposed, including selective apoptosis of abnormal cells, cellular exclusion of aneuploid blastomeres, compartmentalization of abnormal cells into extraembryonic tissues, and chromosomal rescue events (such as trisomic or monosomic rescue), while in some embryos, no correction occurs, leading to persistence of aneuploid cell lineages. Follow-up studies on mosaic embryo transfer outcomes indicate that some embryos can eliminate or segregate aneuploid cells, leading to successful live births. However, the extent to which self-correction occurs, and the precise biological mechanisms underlying these processes, remain poorly understood. The likelihood of successful correction depends on the proportion and distribution of aneuploid cells as current evidence shows that embryos with high-level mosaicism have reduced developmental potential. This mini-review integrates current biological insights into ploidy correction mechanisms with clinical outcome data from mosaic embryo transfers, highlighting both the potential and limitations of embryonic self-correction hypotheses. By examining the interplay between mechanism studies and clinical observations, it underscores the challenges in predicting embryo viability and the necessity for standardized approaches in ART. Future research could help in defining the molecular and developmental pathways governing ploidy correction to improve embryo selection strategies and refine ART guidelines.