Definition of Incompatibility, Rh

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Incompatibility, Rh: The state of mother and fetus having different Rh blood group types so that means their Rh types are "incompatible." The red blood cells of an Rh+ (Rh positive) fetus may in this situation be attacked by antibodies produced by the Rh- (Rh negative) mother. The antibodies pass across the placenta from mother to fetus and the result is hemolytic disease for the fetus and newborn.

Treatment may include watchful waiting, putting the baby "under the light" (under a UV light) or an exchange transfusion. Prevention of hemolytic disease of the newborn is by giving the mother Rh0 (D) immune globulin (brand name: RhoGAM).

History: Hemolytic disease of the fetus and newborn was first described by a French midwife in 1609 in a set of twins: the first twin was hydropic (swollen with edema fluid) and stillborn; the second twin was deeply jaundiced and subsequently died of kernicterus.