Question

Beta hCG is detected earliest in serum by which day of conception?

• A. 8 days
• B. 15 days
• C. 21 days
• D. 30 days

Hint:

Serum picks up hCG before urine does - think roughly a week after conception.

Answer 1

The Correct Option is A

Step 1: Beta hCG (human chorionic gonadotropin) is a glycoprotein hormone secreted by the syncytiotrophoblast of the developing placenta. Its detection forms the basis of all pregnancy tests.

Step 2: hCG begins to be produced very soon after implantation. It can be detected in serum as early as 8 to 9 days after conception, which is the earliest reliable window.

Step 3: In urine, hCG appears later, by about 14 days after conception, because serum levels rise before urinary concentrations become measurable. This is why serum testing is more sensitive and earlier than urine testing.

Step 4: Options of 15, 21 and 30 days are too late for the earliest serum detection, so the correct answer is 8 days.