Rh Incompatibility

Blood type is identified by two major components—a letter (A, B, AB, or O) and the Rh factor. If your blood contains the Rh factor, you are Rh positive; if it lacks this factor, you are Rh negative. Therefore, if your blood type is AB and your are Rh-negative, you are said to have AB-negative blood.

If an Rh-negative person receives Rh Positive blood, she will become sensitized and her body will produce antibodies to attack the foreign red blood cells. This is significant in pregnancy for an Rh negative woman, because if her mate is Rh positive, the child can be Rh positive. During amniocentesis or the delivery of the placenta, it is possible for the baby’s blood to come in contact with the mother’s blood. If this happens, the mother’s body will produce antibodies against the Rh-positive cells.

These antibodies will attack the Rh-positive blood cells and cause them to die. This disease is called hemolytic disease of the newborn. Since the sensitization does not occur until after the birth, the first baby is not affected, unless the woman was previously sensitized and not treated. If a woman is not treated and becomes pregnant again with an Rh-positive baby, the antibodies will cross the placenta and kill the fetus’s red blood cells.


To prevent hemolytic disease of the newborn, RhoGAM, an Rh-immune globulin, is administered, after the birth of an Rh-positive infant, as well as after a miscarriage, an abortion, or amniocentesis. It is also given at 28 weeks of pregnancy. RhoGAM acts by suppressing the specific immune response of Rh-negative individuals to Rh-positive red blood cells. Since the woman does not produce antibodies, subsequent pregnancies will not be affected, and the woman can give birth to healthy newborns in the future. Hemolytic disease of the newborn is rare since the development of RhoGAM.