This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Earliest detection of pregnancy by ultrasound is by 
Select and explain. 
A. Fetal skeleton, B. Fetal node, C. FSH, D. Gestation sac
D: Gestation sac
Answer: D: Gestation sac 
Explanation: The first definitive sonographic finding to suggest pregnancy is visualization of the gestational sac. The first sign of intrauterine pregnancy is presence of yolk sac within the gestational sac.