Definition

Erythroblastosis fetalis, also known as hemolytic disease of the newborn or immune hydrops fetalis, is a disease in the fetus or newborn caused by transplacental transmission of maternal antibody, usually resulting from maternal and fetal blood group incompatibility. Rh incompatibility may develop when a woman with Rh-negative blood becomes pregnant by a man with Rh-positive blood and conceives a fetus with Rh-positive blood. Red blood cells (RBCs) from the fetus leak across the placenta and enter the woman's circulation throughout pregnancy with the greatest transfer occurring at delivery. This transfer stimulates maternal antibody production against the Rh factor, which is called isoimmunization. In succeeding pregnancies, the antibodies reach the fetus via the placenta and destroy (lyse) the fetal RBCs. The resulting anemia may be so profound that the...