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
The one measurement of fetal maturity that is not affected by a 'bloody tap' during amniocentesis is: 
Select and explain. 
A. L/S ratio, B. Phosphatidyl glycerol, C. α-fetoprotein, D. Bilirubin as a measured by DOD 450
B: Phosphatidyl glycerol
Answer: B: Phosphatidyl glycerol 
Explanation: The best test to detect fetal lung maturity in diabetic mothers is presence of phophatidyl glycerol (PG) in amniotic fluid. If PG is present in amniotic fluid fetal lungs are considered mature and vice versa.