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': 'Accurate diagnosis of anencephaly on ultrasound can be done at: September 2005 \nSelect and explain. \nA. 5 weeks of gestation, B. 8 weeks of gestation, C. 10 weeks of gestation, D. 14 weeks of gestation', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C: 10 weeks of gestation In the first half of the pregnancy, the diagnosis is made by the elevated alfa-fetoprotein in amniotic fluid and confirmed by sonography. The findings at 13 weeks are: Absence of cranial vault Angiomatous brain tissue In the later half of the pregnancy the diagnosis is difficult specially when associated with hydramnios.', 'role': 'assistant'}]