ABO hemolytic disease of the fetus and newborn (HDFN) differs from Rh HDFN in that:

ABO hemolytic disease of the fetus and newborn (HDFN) and Rh HDFN are both conditions that can lead to the destruction of fetal red blood cells due to maternal antibodies, but they have distinct differences in their severity and mechanisms.

The correct choice emphasizes that Rh HDFN is generally more severe than ABO HDFN. This difference in severity arises primarily from the nature of the antibodies involved. Anti-Rh antibodies (e.g., anti-D) can cause significant fetal morbidity and mortality because they can lead to rapid hemolysis of fetal red blood cells, often resulting in severe anemia, jaundice, and even fetal hydrops. Conversely, ABO HDFN is typically milder because the anti-A and anti-B antibodies are usually of the IgM class, which do not cross the placenta efficiently. When IgG anti-A/B antibodies are present, they tend to be less aggressive than the anti-Rh antibodies, leading to milder clinical manifestations.

Understanding this distinction is crucial for effective management and treatment options for affected newborns, as Rh HDFN often requires more intensive intervention than ABO HDFN.