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
In Erythroblastosis fetalis, the first child is spared because: 
Select and explain. 
A. Immune response in second exposure is fast, B. Sensitization of Rh-negative mothers by a Rh-positive fetus generally occurs at bih, C. Small amounts of fetal blood leak into the ma ternal circulation at the time of delivery, D. Mothers develop significant titers of anti-Rh ag glutinins during the postpaum period
B: Sensitization of Rh-negative mothers by a Rh-positive fetus generally occurs at bih
Answer: B: Sensitization of Rh-negative mothers by a Rh-positive fetus generally occurs at bih 
Explanation: Sensitization of Rh-negative mothers by a Rh-positive fetus generally occurs at bih