When a mothers blood type is Rh-negative and her fetus blood type is Rh-positive, it is called Rh incompatibility. This can lead to Rh-induced hemolytic disease of the newborn, also known as erythroblastosis fetalis. In addition, if a babys and mothers blood are incompatible, it can lead to fetal anemia, immune hydrops, and other complications. The two blood types that are not compatible for pregnancy are:

• Rh-negative mother and Rh-positive father: If a woman who is Rh-negative and a man who is Rh-positive conceive a baby, the fetus may have Rh-positive blood, inherited from the father. About half of the children born to an Rh-negative mother and Rh-positive father will be Rh-positive.

• Mother with type O blood and baby with type A or B blood: Sometimes an incompatibility may happen when the mother is blood type O and the baby is either A or B. This can affect the babys red blood cells and cause complications.

It is important for Rh-negative mothers to be followed closely by their healthcare providers during pregnancy to prevent Rh incompatibility. Special immune globulins, called RhoGAM, are now used to prevent RH incompatibility in mothers who are Rh-negative. Blood type incompatibility can be prevented with a blood test early in pregnancy. If an incompatibility is found, an Rh-immune globulin treatment is administered about 28 weeks into the pregnancy.