This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
[{'content': 'At how many weeks of gestation is amniocentesis mostly performed ? \nSelect and explain. \nA. 10-12 weeks, B. 12-20 weeks, C. 20-25 weeks, D. 25-30 weeks', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Amniocentesis is often performed between 15 and 20 weeks of gestation. Chorionic villus sampling (CVS) is an alternative to amniocentesis and is usually performed either transervically or trans abdominally between 10 and 12 weeks of gestation .', 'role': 'assistant'}]