A 42-year-old pregnant woman undergoes amniocentesis that reveals trisomy 21. Which of the following maternal factors most likely contributed to this chromosomal abnormality?
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✓ Correct answer: B. Advanced maternal ageAdvanced maternal age (typically defined as age 35 or older) is the most significant risk factor for trisomy 21 (Down syndrome). The risk increases exponentially with maternal age due to aging oocytes being more susceptible to nondisjunction during meiosis, which leads to trisomy 21 in the fetus.
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