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': 'Prenatal diagnosis at 16 weeks of pregnancy can be performed using which of the following: \nSelect and explain. \nA. Amniotic fluid, B. Maternal blood AFP, C. Chorionic villi, D. Fetal blood', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Amniocentesis is done during 16th week of pregnancy. Fetal blood sampling is done after 17-18 weeks, chorionic villi during 11-12 weeks of pregnancy, maternal blood AFP during 15-20 weeks. Ref: Textbook of Gynaecology By Dutta, 6th Edition, Page 108; In-Vitro Feilization By Kay Elder, Brian Dale, Yves Menezo, Joyce Harper, John Huntriss, 2010, Page 243; Donald School Textbook of Ultrasound in Obstetrics and Gynecology By Asim Kurjak, 2008, Page 755.', 'role': 'assistant'}]