This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Twin Pregnancy, Molar Pregnancy, Gestational Trophoblastic disease and contraception in special situations (Sour Grapes!), Subject name: Gynaecology & Obstetrics
A 23 year old pregnant lady at 16 weeks pregnancy had vaginal spotting. She was found to have a uterus enlarged to 28 weeks' size and no fetal hea sound audible with the fetal Doppler. Human chorionic gonadotropin (hCG) serum levels are 1,00,000 miu/mL. Which of the following tests is most appropriate at this time? 
Select and explain. 
A. Serial clotting function studies, B. Pelvic ultrasound, C. Serial hCG estimation, D. Apt test on vaginal blood
B: Pelvic ultrasound
Answer: B: Pelvic ultrasound 
Explanation: A uterus dis-propoionately larger than the period of pregnancy is a strong possibility of hydatidiform mole. Serial hCG would be elevated well beyond normal levels. Ultrasound will show classic signs of molar tissue and is the test of choice. The Apt test is to detect fetal hemoglobin, of which there is none in complete molar pregnancies. Serial clotting function will not help in the immediate diagnosis