Anatomy General obstetrics 2202281e What is seen earliest in USG? A Yolk sac B Fetal hea C Chorion D Placenta High-Yield 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.