Aneuploidy in oocytes from women of advanced maternal age: analysis of the causal meiotic errors and impact on embryo development.

This article focuses on the mechanisms leading to aneuploidy in oocytes from women of advanced maternal age (AMA, 36–40 years) and its association with embryo development. Using data from the multicentre randomized controlled trial ESTEEM, which applied preimplantation genetic testing for aneuploidy (PGT-A) via array comparative genomic hybridization (aCGH) on polar bodies (PBs), the study found that known meiotic errors—primarily precocious separation of sister chromatids (PSSC) in Meiosis I and non-disjunction (ND) in Meiosis II or reverse segregation (RS)—accounted for 90.4% of abnormal chromosome copy numbers. Aneuploidy was associated with decreased embryo quality from Day 3 to Day 5 post-insemination, while PB biopsy itself did not adversely affect embryo morphology. The study also identified a subset of unexplained chromosome segregation patterns, suggesting that current understanding of aneuploidy mechanisms in oocytes is incomplete.