This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
What is seen earliest in USG? 
Select and explain. 
A. Yolk sac, B. Fetal hea, C. Chorion, D. Placenta
A: Yolk sac
Answer: A: Yolk sac 
Explanation: Yolk sac is the first anatomic structure seen within gestational sac. By TVS, it can be seen as early as 5.5week By TAS, it is seen by 7 weeks. Ref:Datta Obs 9e pg 601.