Definition of Rh incompatibility

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Rh incompatibility: The difference in Rh blood group types between an Rh negative mother and her Rh positive baby that leads to hemolytic disease of the newborn. The mother and baby's Rh blood group types are therefore said to be "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 of 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, and the second of the twins was deeply jaundiced and subsequently died of kernicterus.