Immunization of an individual against the blood group antigens (e.g., Rh antigens) of another individual.

Incompatibility of blood type between the mother and her fetus.

The development of antibodies (isoantibodies) within an individual against antigens from another individual of the same species.

Active immunization of an individual against blood from an individual of the same species, especially the production of anti-Rh antibodies by Rh-negative mothers against red fetal blood cell antigens. During maternal trauma, loss of pregnancy (abortion), or delivery, some of the infant’s blood is transferred to the mother, stimulating antibody production. If a second child is Rh-positive, the mother’s anti-Rh antibodies will cross the placenta and cause hemolytic disease of the newborn.