DefinitionErythroblastosis fetalis is a potentially life-threatening blood disorder in a fetus or newborn infant. This article provides a general overview. For more detailed information see the specific disorder:ABO incompatibilityRh incompatibilityAlternative NamesHemolytic disease of the newbornCauses, incidence, and risk factorsErythroblastosis fetalis develops in an unborn infant when the mother and baby have different blood types. The mother produces substances called antibodies that attack the developing baby's red blood cells.The most common form of erythroblastosis fetalis is ABO incompatibility, which can vary in severity.The less common form is called Rh incompatibility, which can cause very severe anemia in the baby.SymptomsSymptoms in a newborn baby may include:AnemiaEdema (swe