This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics And Gynaecology, Subject name: Radiology
[{'content': 'Earliest sign of pregnancy on TVS is? \nSelect and explain. \nA. Gestational sac, B. Fetal pole, C. Yolk sac, D. Fetal heart sounds', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., Gestational sac "The first definitive Sonographic finding to suggest early pregnancy is visualization of gestational sac" - Callen 4th/e p. 114* The gestational sac can be visualized as early 4Vi weeks of gestation and the yolk sac at about five weeks.* The gestational sac can be visualized as early as 4Vi weeks by transvaginal USG and 5 weeks by transabdominal USG.* Fetal heart rate can be detected by TVS at 5-6 weeks.', 'role': 'assistant'}]