erythroblastosis fetalis /-blastō″sis/ [Gk, erythros + blastos, germ, osis, condition; L, fetus, bringing forth] , a type of hemolytic anemia in newborns that results from maternal-fetal blood group incompatibility, specifically involving the Rh factor and the ABO blood groups. The condition is caused by an antigen-antibody reaction in the bloodstream of the infant resulting from placental transmission of maternally formed antibodies against the incompatible antigens of the fetal blood. In Rh factor incompatibility, the hemolytic reaction occurs only when the mother is Rh negative and the infant is Rh positive. The isoimmunization process rarely occurs in the first pregnancy, but there is increased risk with each succeeding pregnancy. See also hydrops fetalis, hyperbilirubinemia of the newborn, Rh factor, hemolytic disease of the fetus and newborn.
