The article reviews the mechanisms and new insights into human aneuploidy, a condition where embryos have an abnormal number of chromosomes. Aneuploidy, which accounts for at least 10% of human pregnancies, is more common in older women and is often due to errors in maternal meiosis. Recent studies have revealed the complexity of meiotic defects, showing that the age-related increase in errors is not due to a single factor but to a combination of unique features of oogenesis and various endogenous and exogenous factors. The article discusses the incidence and etiology of aneuploidy in human eggs and embryos, sex-specific differences in meiotic cell cycle checkpoints, and the potential influence of environmental agents on aneuploidy rates. It highlights the importance of recombination and sister chromatid cohesion in preventing aneuploidy, and the role of the spindle assembly checkpoint in controlling meiotic division. The article also explores the impact of assisted reproductive technology (ART) on aneuploidy rates and the potential effects of endocrine disruptors like bisphenol A (BPA). Finally, it emphasizes the need for further research to understand the hormonal signals controlling meiosis and the role of environmental factors in aneuploidy.The article reviews the mechanisms and new insights into human aneuploidy, a condition where embryos have an abnormal number of chromosomes. Aneuploidy, which accounts for at least 10% of human pregnancies, is more common in older women and is often due to errors in maternal meiosis. Recent studies have revealed the complexity of meiotic defects, showing that the age-related increase in errors is not due to a single factor but to a combination of unique features of oogenesis and various endogenous and exogenous factors. The article discusses the incidence and etiology of aneuploidy in human eggs and embryos, sex-specific differences in meiotic cell cycle checkpoints, and the potential influence of environmental agents on aneuploidy rates. It highlights the importance of recombination and sister chromatid cohesion in preventing aneuploidy, and the role of the spindle assembly checkpoint in controlling meiotic division. The article also explores the impact of assisted reproductive technology (ART) on aneuploidy rates and the potential effects of endocrine disruptors like bisphenol A (BPA). Finally, it emphasizes the need for further research to understand the hormonal signals controlling meiosis and the role of environmental factors in aneuploidy.