Professional and Linguistic Assessments Board (PLAB) Practice Exam

When is the best time to administer anti-D immunoglobulin after delivery?

1. Within 24 hours

2. As soon as possible within 72 hours

3. Within one week

4. During the first postpartum visit

The correct answer is: As soon as possible within 72 hours

Administering anti-D immunoglobulin after delivery is primarily aimed at preventing Rh immunization in Rh-negative mothers who deliver Rh-positive infants. The key reason why the best time to administer it is as soon as possible within 72 hours of delivery is that this window ensures that any Rh-positive fetal blood that may enter the mother's circulation is neutralized before her immune system can develop antibodies against the Rh factor. The administration of anti-D immunoglobulin within this timeframe effectively reduces the risk of sensitization, which could lead to complications in future pregnancies. Prompt administration is crucial because the immune response can begin fairly quickly after exposure. While administering it within 24 hours could be effective, the guidelines emphasize that the critical window for preventing sensitization is within 72 hours. This considers both practical hospital protocols and the physiological response of the mother’s immune system. Delays beyond this period greatly increase the risk of sensitization, potentially affecting future pregnancies and leading to conditions such as hemolytic disease of the newborn in subsequent Rh-positive pregnancies. The other options, such as administering it within one week or during the first postpartum visit, do not adequately address the need for timely intervention, as the risks of sensitization become materially higher if the immunoglobulin