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: Gynaecology & Obstetrics
Most impoant investigation for ectopic pregnancy: 
Select and explain. 
A. Serial f3-hCG levels, B. Transvaginal USG, C. Progesterone measurement, D. Culdocentesis
B: Transvaginal USG
Answer: B: Transvaginal USG 
Explanation: If TVS reveals an intrauterine gestational sac,the diagnosis of ectopic can usually be ruled out .sometimes a psuedosac may be seen in an ectopic due to bleeding produced by separation of a decidual cast.(refer pgno:159 sheila 2 nd edition)