What is a significant risk factor for a woman having a child with Down syndrome?

Advanced maternal age is a well-established significant risk factor for having a child with Down syndrome. As a woman's age increases, particularly after the age of 35, the likelihood of chromosomal abnormalities, such as an extra copy of chromosome 21 that causes Down syndrome, also increases. This increased risk is thought to be due to age-related changes in the eggs, particularly in the processes of cell division that lead to the formation of eggs and sperm. As the maternal age advances, the probability of nondisjunction—where the chromosomes fail to separate properly during cell division—rises, leading to a higher chance of the resulting embryo having an abnormal number of chromosomes.

In contrast, while smoking during pregnancy, family history of diabetes, and obesity can pose risks to maternal and fetal health in various ways, they are not directly associated with an increased risk of Down syndrome in the offspring. Thus, understanding the implications of maternal age is crucial in prenatal counseling and risk assessment for chromosomal conditions like Down syndrome.