This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal Imaging, Subject name: Gynaecology & Obstetrics
[{'content': 'Yolk sac is seen earliest at what stage of gestational age- \nSelect and explain. \nA. 5 .5 weeks, B. 7.5 weeks, C. 10 weeks, D. 12.5 weeks', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 4a' i.e., 5[?]5 weeks o Using transvaginal sonography, yolk sac always visible at 5[?]5 weeks gestational age. (when mean sac diameter- 5 - 8 mm).o Using transabdominal approach, yolk sac should be evident by 7 weeks gestation, when mean sac diameter is 20 mmo Cardiac activity should be detected at 6 - 6-5 weeks gestation by TVS and 8 weeks by using TAS.", 'role': 'assistant'}]