This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Medicine
Alpha-fetoprotein in maternal serum and/or amniotic fluid is increased in all except 
Select and explain. 
A. Fetal neural tube defects, B. Down's syndrome, C. Anencephaly, D. Encephalocele
B: Down's syndrome
Answer: B: Down's syndrome 
Explanation: In Down syndrome, the AFP is decreased in the mother's blood, presumably because the yolk sac and fetus are smaller than usual. Estriol is a hormone produced by the placenta, using ingredients made by the fetal liver and adrenal gland. Estriol is decreased in the Down syndrome pregnancy Ref Robbins 9/e pg 170