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': 'Amniocentesis is done at what intrauterine age? \nSelect and explain. \nA. 12-Oct, B. 20-Dec, C. 20-25, D. 25-30', 'role': 'user'}, {'content': "Answer: B \nExplanation: ANSWER: (B) 12-20REF: Current OB./GYN 10th edition chapter 13.Repeat from December 2011 & June 2008Amniocentesis is often performed between 15 and 20 weeks' gestation. Chorionic villus sampling (CVS) is an alternative to amniocentesis. It is performed between 10 and 12 weeks' gestation and can be performed either transcervically or transabdominally.", 'role': 'assistant'}]