Aneuploidy and Pregnancy Loss in Humans

Pregnancy loss is a common and major problem in human reproduction. Its cause largely is chromosomal anomaly, especially aneuploidy. There is a significant gender difference in gamete production in humans. On average, one in four eggs produced by women is chromosomally abnormal, and the frequency of abnormal gametes increases sharply with age, especially in those aged 35 years or older. While a vast majority of embryos with aneuploidy aborts in utero, a small percentage (∼10%) is born live. These are the sex chromosomes (X and Y) and those with trisomy of the gene-poor chromosomes, viz., chromosomes 21, 18, and 13, though these too suffer from disabilities. The major causes of aneuploidy are non-disjunction, lack of recombination, premature separation of chromatids/kinetochores, and RS. These anomalies arise due to poor surveillance of the meiotic process as well as the loss of cohesion between chromosomes in female gametogenesis.