This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Alpha feto protein levels are increased in all EXCEPT: 
Select and explain. 
A. Open neural tube defects, B. Down syndrome, C. Twin pregnancy, D. Intrauterine death
B: Down syndrome
Answer: B: Down syndrome 
Explanation: AFP is measured in pregnant women through the analysis of maternal blood or amniotic fluid, as a screening test for a subset of developmental abnormalities: it is principally increased in open neural tube defects and omphalocele and is decreased in Down syndrome.