This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis in obstetrics, Subject name: Gynaecology & Obstetrics
The best way of diagnosing Trisomy 21 during second trimester of pregnancy is: 
Select and explain. 
A. Triple marker estimation, B. Nuchal skin fold thickness measurement, C. Chorionic villus sampling, D. Amniocentesis
D: Amniocentesis
Answer: D: Amniocentesis 
Explanation: The main use is in diagnosing chromosomal disorders like trisomy 21.Amniotic fluid cells are cultured and karyotyping done,which may take up to 3 weeks (refer pgno:502 sheila textbook of obstetrics 2 nd edition)