This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis in obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'The best way of diagnosing Trisomy 21 during second trimester of pregnancy is: \nSelect and explain. \nA. Triple marker estimation, B. Nuchal skin fold thickness measurement, C. Chorionic villus sampling, D. Amniocentesis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The main use is in diagnosing chromosomal disorders like trisomy 21.Amniotic fluid cells are cultured and karyotyping done,which may take up to 3 weeks (refer pgno:502 sheila textbook of obstetrics 2 nd edition)', 'role': 'assistant'}]