Under what condition does Rh isoimmunization occur?

• A. If mom is Rh positive and baby is Rh negative
• B. If mom is Rh negative and baby is Rh positive
• C. If both parents are Rh positive
• D. If mom is Rh negative with no family history of Rh factor

Answer: (B)

Rh isoimmunization occurs when an Rh-negative mother has an Rh-positive baby. This condition arises when the baby's Rh-positive red blood cells enter the mother's circulation, often during delivery or through fetal-maternal bleeding during pregnancy.

In this scenario, the Rh-negative mother may produce antibodies against the Rh factor, a protein found on the surface of Rh-positive red blood cells. If these antibodies develop, they can cross the placenta in subsequent pregnancies, potentially leading to hemolytic disease of the newborn in future Rh-positive babies. The key factor here is the incompatibility between the Rh status of the mother and the baby, which leads to an immune response.

Other scenarios do not produce Rh isoimmunization. For instance, if both parents are Rh positive, or if the mother is Rh negative with no prior exposure to Rh-positive blood, there is no risk of isoimmunization occurring.