This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Gynaecology & Obstetrics
[{'content': 'At 35years Maternal age-related risk for Down syndrome in singleton pregnancy at midtrimester is \nSelect and explain. \nA. 1 in 31, B. 1 in 69, C. 1 in 149, D. 1 in 250', 'role': 'user'}, {'content': "Answer: D \nExplanation: Maternal Age-Related Risk for Down Syndrome at Midtrimester in Singleton PregnanciesAgeMidtrimester351/250371/149401/69411/53421/41431/31441/25451/19(Ref: William's Obstetrics; 25th edition)", 'role': 'assistant'}]