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
What is the best time to give anti-D to a pregnant patient? 
Select and explain. 
A. 12 weeks, B. 28 weeks, C. 36 weeks, D. After delivery
B: 28 weeks
Answer: B: 28 weeks 
Explanation: Ans: B. 28 weeks (Ref Williams 24/e p312: COGT 11/e p353; FERNANDO ARIAS 4/e p374).Best time to give anti-D to a pregnant patient is 28 weeks.According to American College of Obstetricians and Gynecologists, 2010:Anti-D immune globulin is given prophylactically to all Rh D-negative, unsensitized women at approximately 28 weeks.Second dose is given after delivery if the infant is Rh D-positive .