Final Answer:
Most women who give birth to a child with Down syndrome are under the age of 40. Thus, the correct answer is 2) Under age 40.
Step-by-step explanation:
The likelihood of having a child with Down syndrome increases with the mother's age, particularly after the age of 35. However, statistically, more children with Down syndrome are born to women under the age of 35 simply because this age group has a higher number of pregnancies overall.
When we consider the absolute numbers, more births happen in younger age groups, so even though the likelihood of Down syndrome increases with maternal age, the majority of children with Down syndrome are born to mothers under 40.
To delve into the probabilities, research indicates that the risk of having a child with Down syndrome rises as a woman gets older. For instance, at age 25, the probability of having a child with Down syndrome is about 1 in 1,250; by age 40, the probability increases to about 1 in 100.
However, due to the higher number of pregnancies occurring in younger age groups, more children with Down syndrome are born to mothers under the age of 40. This doesn't discount the increased risk associated with advanced maternal age, but it clarifies that the majority of children with Down syndrome are born to younger mothers due to the larger number of pregnancies in that demographic.
Therefore, while the risk of Down syndrome does rise with maternal age, the majority of cases occur in women under 40 due to the sheer volume of pregnancies in that age group compared to those over 40.
Thus, the correct answer is 2) Under age 40.