This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2018, Subject name: Gynaecology & Obstetrics
Which of the following markers is not used in quadruple test for antenatal detection of Down syndrome? 
Select and explain. 
A. AFP, B. ss-hCG, C. Estradiol, D. Inhibin
C: Estradiol
Answer: C: Estradiol 
Explanation: Quadruple test is the second trimester measurement of maternal serum 1 Alpha fetoprotein ( MSAFP) : decreased2 unconjugated estriol: decreased3 HCG: increased4 Inhibin A : increased - It is done between 15 - 20 weeks