Pathophysiology
Clinical meaning
Rh alloimmunization occurs when a pregnant patient with Rh-negative blood is exposed to Rh-positive fetal red blood cells. This exposure triggers the maternal immune system to produce anti-D antibodies because it does not recognize the Rh (D) antigen on fetal RBCs. In a first pregnancy, the response is typically mild (IgM). However, in subsequent pregnancies with an Rh-positive fetus, the sensitized immune system mounts a rapid IgG response that crosses the placenta and destroys fetal RBCs, causing hemolytic disease of the fetus and newborn (HDFN). Prevention involves administering Rh immune globulin (RhoGAM) to unsensitized Rh-negative patients. The nurse assists with monitoring and supports the care plan as directed.