This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intra Uterine Growth Restriction, Intrapaum and Antepaum Fetal Surviellance, Subject name: Gynaecology & Obstetrics
Chorionic villous sampling is needed in all except 
Select and explain. 
A. Neural tube defects, B. Downs syndrome, C. Thalassemia, D. noonan syndrome
A: Neural tube defects
Answer: A: Neural tube defects 
Explanation: Chorionic villous sampling(CVS) is done at the 10 - 13 week of gestation to diagnose conditions which could be debilitating or life threatening for the unborn fetus. Neural tube defects are best assessed at a later gestation around 20 weeks though the earliest to be picked up is ANENCEPHALY which can be picked up by 10-12 weeks with USG. The most specific indicator for Neural tube defects is the acetylcholinesterase