Rh incompatibility is a condition that occurs during pregnancy if a woman has Rh-negative blood and her baby has Rh-positive blood. Rh-negative and Rh-positive refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells. If you have Rh factor, youre Rh-positive. If you dont have it, youre Rh-negative. Rh factor is inherited (passed from parents to children through the genes). Most people are Rh-positive. Whether you have Rh factor doesnt affect your general health. However, it can cause problems during pregnancy. Overview When youre pregnant, blood from your baby can cross into your bloodstream, especially during delivery. If youre Rh-negative and your baby is Rh-positive, your body will react to the babys blood as a foreign substance. Your body will create antibodies (proteins) against the babys Rh-positive blood. These antibodies usually dont cause problems during a first pregnancy. This is because the baby often is born before many of the antibodies develop. However, the antibodies stay in your body once they have formed. Thus, Rh incompatibility is more likely to cause problems in second or later pregnancies (if the baby is Rh-positive). The Rh antibodies can cross the placenta and attack the babys red blood cells. This can lead to hemolytic anemia (HEE-moh-lit-ick uh-NEE-me-uh) in the baby. Hemolytic anemia is a condition in which red blood cells are destroyed faster than the body can replace them. Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, your baby wont get enough oxygen. This can lead to serious problems. Severe hemolytic anemia may even be fatal to the child. Outlook With prompt and proper prenatal care and screening, you can prevent the problems of Rh incompatibility. Screening tests allow your doctor to find out early in your pregnancy whether youre at risk for the condition. If youre at risk, your doctor will carefully check on you and your baby throughout your pregnancy and prescribe treatment as needed. Injections of a medicine called Rh immune globulin can keep your body from making Rhantibodies. This medicine helps prevent the problems of Rh incompatibility. If youre Rh-negative, youll need this medicine every time you have a baby with Rh-positive blood. Other events also can expose you to Rh-positive blood, which could affect a pregnancy. Examples include a miscarriage or blood transfusion. If youre treated with Rh immune globulin right after these events, you may be able to avoid Rh incompatibility during your next pregnancy. 
What is (are) Rh Incompatibility ?