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
During which gestational age is peak serum HCG levels attained ? 
Select and explain. 
A. 7-9 weeks, B. 11-13 weeks, C. 20 weeks, D. 25 weeks
A: 7-9 weeks
Answer: A: 7-9 weeks 
Explanation: Human chorionic gonadotropin Glycoprotein with alpha and beta chains 3 subunit is specific to hCG Secreted by trophoblastic tissue, some amount by fetal tissues, adult ant pituitary Many isoforms of hCG with variable crossreactivity between various assays More than loo commercial assays Sandwich type immunoassay: Sens - 1 IU/ml Immuno radiometric assays: more Sensitive Ref : Dutta book of obstetrics 8th Ed.