In cases of Rh incompatibility, a baby's red blood cells have a substance called the Rh D factor, and the mother's blood cells do not. In medical terms, the baby is Rh positive and you are Rh negative. If some of the baby's red blood cells leak into your system, your body may produce antibodies to the Rh D factor (a condition called sensitization). These antibodies can cross the placenta and destroy the red blood cells in your unborn baby or in the next Rh-positive baby you have.

How does it occur?

Rh incompatibility occurs only if you are Rh negative and your baby is Rh positive. It does not occur if you are Rh positive and your baby is Rh negative. In most cases you will not be exposed to the baby's blood until you give birth. This usually means that your first baby is not affected. However, large amounts of the baby's blood often leak into the mother during delivery. If you are Rh negative, the next Rh-positive baby you have could have problems if you have developed antibodies. Occasionally, in the following situations, some of the baby's blood may leak into your system during pregnancy:

• After amniocentesis or other invasive procedure
• During a miscarriage or abortion
• During an ectopic pregnancy
• If you bleed heavily during pregnancy.

If you are Rh negative and you received Rh-positive blood in a transfusion, you may have developed antibodies that will cause Rh incompatibility. In most cases, development of antibodies (sensitization) can be prevented, but if antibodies are formed, they will cross the placenta and can cause serious damage to the red blood cells of an Rh-positive baby.

What are the symptoms?

You will have no symptoms. Symptoms and signs of the problem are seen in the baby if he or she develops hemolytic disease. In this condition, the baby's red blood cells start to break down, causing anemia. The baby may have other problems due to the anemia, such as jaundice and, after birth, breathing problems. The baby might even die in the womb if too much of the baby's blood is destroyed.

How is it diagnosed?

Women at risk for Rh incompatibility can be identified with the routine blood tests done at prenatal visits with the doctor. The tests include:

• Blood type
• Rh type
• Antibody screening

If you are Rh negative and have antibodies against the Rh D factor, Rh incompatibility may be a problem. If you are Rh negative, the blood of the baby's father should be tested. If the father's blood is Rh positive, the baby has a chance of inheriting Rh-positive blood from the father. If the father is Rh negative, there will not be a problem because the baby will have no chance of inheriting Rh-positive blood.

Some of the tests used to diagnose and assess hemolytic disease in the baby before and after birth are:

• Amniocentesis
• Cordocentesis
• Ultrasound
• Non-stress tests
• Blood tests

How is it treated?

If you have already been sensitized by a previous birth, your baby may develop hemolytic disease before birth. If this happens, your baby may need a blood transfusion in the womb before birth. Sometimes early delivery by cesarean section is necessary.

If you have not been sensitized, you will be given an injection of Rh-immune globulin at about 28 weeks of pregnancy, and within 72 hours after a birth, miscarriage, abortion, or amniocentesis. The Rh-immune globulin contains antibodies to the Rh D factor. These antibodies will destroy any red blood cells from the baby that have entered your blood. You will not have a chance to form your own antibodies to the Rh D factor. If you receive the injection at 28 weeks and after delivery, sensitization will be prevented and Rh incompatibility should not be a problem during your next pregnancy.

It is important to receive Rh-immune globulin in all cases when the baby's blood could leak into your system, including:

• All pregnancies including ectopic (tubal) pregnancies
• Early miscarriages
• After chorionic villus sampling
• After amniocentesis

How long will the effects last?

Sensitization usually doesn't happen until after the birth of an Rh-positive baby. Therefore, in most cases Rh incompatibility is not a problem during a woman's first pregnancy and delivery of an Rh-positive baby. However, later pregnancies and deliveries may be affected unless the mother is treated with Rh-immune globulin after EVERY birth, miscarriage, and abortion. Sensitization is permanent and the effects are usually worse with each subsequent pregnancy.

What can be done to help prevent problems associated with Rh incompatibility?

This complication of pregnancy has not occurred often since the discovery of Rh-immune globulin (also called RhoGAM). Rh-immune globulin can prevent sensitization. It is given to an Rh-negative woman shortly after every delivery, miscarriage, or abortion. It is also given to a pregnant Rh-negative woman after amniocentesis, any bleeding episodes, and during the seventh month of pregnancy

Angelia Fenton is mom to four, interested all things family, and in new computer and web technologies. She serves as Assistant Community Manger and Technical Liaison at Pregnancy.org.

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