This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis of Pregnancy, Subject name: Gynaecology & Obstetrics
Which of these embryonic structures is the earliest seen USG indicator of pregnancy : 
Select and explain. 
A. Fetal pole, B. Fetal hea activity, C. Gestation sac, D. Fetal skeleton
C: Gestation sac
Answer: C: Gestation sac 
Explanation: Gestational sac cardiac activity Trans vaginal scan (TVS) 4+ weeks 5+ weeks Trans abdominal scan (TAS) 5 + weeks 6 + weeks