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': 'Earliest detection of pregnancy by ultrasound is by \nSelect and explain. \nA. Fetal skeleton, B. Fetal node, C. FSH, D. Gestation sac', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The first definitive sonographic finding to suggest pregnancy is visualization of the gestational sac. The first sign of intrauterine pregnancy is presence of yolk sac within the gestational sac.', 'role': 'assistant'}]