Erythroblastosis fetalis is two potentially disabling or fatal blood disorders in infants: Rh incompatibility disease and ABO incompatibility disease. These disorders are caused by incompatibility between a mother's blood and her unborn baby's blood and may be apparent before birth. Because of the incompatibility, the mother's immune system destroys the baby's blood cells, and the baby suffers severe anemia (deficiency in red blood cells), brain damage, or death. A person's blood type is determined by genes inherited from parents: proteins called antigens in red blood cells and the presence or absence of the Rh-factor. Blood is classified as A, B, AB, or O and positive or negative (e.g., A-positive or B-negative). Blood type doesn't affect health, but the immune system accepts only the individual's blood type or a close match. Introduction of a radically different blood type causes the immune system to produce antibodies that...