In a Rh-negative woman with vaginal bleeding before 12 weeks gestation, what is the indicated Rhogam dose?

• A. 50 μg
• B. 300 μg
• C. 150 μg
• D. 600 μg

Answer: (A)

The key idea is that Rhogam dosing depends on how much fetal red blood cells enter the maternal circulation, which correlates with both gestational age and the severity of the event. In early pregnancy, the amount of fetal blood that can cross into the mother is typically small, so a smaller prophylactic dose is sufficient to prevent maternal sensitization to the Rh(D) antigen. Therefore, a low dose—50 μg—is indicated after vaginal bleeding before 12 weeks in an Rh-negative mother. Larger doses (for example, 300 μg or 600 μg) are used later in pregnancy or after events likely to cause a larger fetal-maternal hemorrhage, and if there’s a significant bleed, a test-guided approach can adjust the dose accordingly.