What is the relationship between maternal age and the probability of giving birth to a child with Down syndrome?

• A. Increased maternal age increases risk
• B. Decreased maternal age increases risk
• C. Age has no effect on risk
• D. Paternal age determines all risk

Answer: (A)

The relationship being tested is how maternal age affects the likelihood of Down syndrome. Down syndrome most often results from nondisjunction during the mother’s egg formation. As a woman’s eggs age, the cellular mechanisms that separate chromosomes during meiosis become more error-prone. If an egg with an extra chromosome 21 is fertilized, the embryo has trisomy 21, leading to Down syndrome. This risk increases with advancing maternal age, especially after age 35, which is why older maternal age is associated with higher probability. Paternal age is not the primary determinant of this risk, and age does affect risk, so the correct understanding is that increased maternal age increases risk.