ABO incompatibility occurs when a pregnant woman has a blood type that is incompatible with her fetus's blood type. It can cause hemolytic disease of the newborn (HDN) when the mother's IgG antibodies destroy the fetus's or newborn's red blood cells. The most common form is ABO HDN, which usually results in mild symptoms and does not require treatment. It occurs when an O group mother has an A or B group baby and the mother's anti-A or anti-B antibodies destroy the baby's red blood cells. Investigations of the mother and baby include blood typing and testing the mother's serum for IgG antibodies, while the baby may experience jaundice, anemia and other symptoms. Treatment