Anti-Rh(D) IgG subclasses and severity of Rh hemolytic disease of the newborn.

The influence of anti-Rh(D) IgG subclasses on the severity of hemolytic disease of the newborn was examined in 98 pregnancies. Disease was severe in 19 of 32 cases in which only IgG1 was detected, 40 of 63 cases in which IgG1 and IgG3 were found and 0 of 3 cases in which only IgG3 was detected. When both IgG1 and IgG3 anti-D were present, hemolytic disease was more severe than when IgG1 alone was detected. The earliest onset of hydrops was at 20 weeks gestation in the IgG1 + IgG3 anti-Rh group, and at 27 weeks gestation in the IgG1 group.