Any condition resulting in the abnormal destruction of fetal blood products, but commonly refers to Rh incompatibility between a mother and fetus. In the Rh incompatibility type of hemolytic disease of the newborn, some infants who can break down red blood cells coated with maternal antibody into hemoglobin and then into indirect bilirubin may lack the final enzyme necessary to convert the latter into harmless, excretable bilirubin; bilirubin thus accumulates in toxic amounts in brain tissues, causing kernicterus and jaundice (see Rhesus isoimmunization; aka erythroblastosis fetalis). The ABO form of HDN also results in destruction of the erythrocytes of a fetus, a condition roughly twice as common as the Rh-incompatibility form of HDN, but is almost always clinically milder in its manifestation, and is caused by some of the smaller anti-A or anti-B antibodies in a mother’s immune system that can permeate the placental membranes, causing jaundice, anemia, and an enlarged liver and spleen. HDN can also be a clinical feature of the Diego, Duffy, Kell-Cellano, and Gerbich blood groups. are also responsible for other hemoglobinopathies.

See fetal hemoglobin, hereditary persistence.

Cf. thalassemia.