This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Gynaecology & Obstetrics
With a sensitive test, hCG can be detected in maternal serum or urine by ------ after ovulation? 
Select and explain. 
A. 3 to 4 days, B. 8 to 9 days, C. 12 to 14 days, D. 20 to 21 days
B: 8 to 9 days
Answer: B: 8 to 9 days 
Explanation: Detection of hCG in maternal blood and urine is the basis for endocrine assays of pregnancy. Syncytiotrophoblasts produce hCG in amounts that increase exponentially during the first trimester following implantation. With a sensitive test, the hormone can be detected in maternal serum or urine by 8 to 9 days after ovulation. The doubling time of serum hCG concentration is 1.4 to 2.0 days. (Ref: William's Obstetrics; 25th edition)