Final answer:
The risk of having a baby with Down syndrome increases with maternal age, primarily due to the increased frequency of chromosomal nondisjunction events in the eggs of older women.
Step-by-step explanation:
The risk of a baby being born with Down's syndrome, also known as trisomy 21, increases with the maternal age. This condition occurs when there are three copies of chromosome 21 instead of the usual two. One of the most recognized risk factors for Down syndrome is advanced maternal age, particularly over the age of 35. Several factors contribute to this increased risk. With age, the likelihood of nondisjunction events during the process of cell division in eggs, or meiosis, increases, which can lead to an extra chromosome 21. This chromosomal nondisjunction is more common in older ova, which have been present in a woman’s ovaries since her own fetal development.
It is not that age increases the number of sex chromosomes or that the placenta delivers oxygen less efficiently. Nor is it due to improved medical interventions. Rather, it is the increased potential for errors in chromosomal separation during the formation of reproductive cells in older women. These errors can result in a developing embryo with three copies of chromosome 21, which leads to Down syndrome.
Figure 15.11 from the American Family Physician publication shows a marked increase in the incidence of Down syndrome associated with maternal age, underscoring the significance of age as a risk factor. It is important to note that while individuals with Down syndrome may have medical and developmental challenges, they can also lead fulfilling lives and contribute to society in meaningful ways.