Rh Incompatibility

What is Rh incompatibility?

If you are a mother with Rh incompatibility, there is a substance on the surface of your baby's red blood cells that is not on your blood cells. This substance is called the Rh factor. People who have the Rh factor are Rh positive. People who do not have it are Rh negative. Being Rh negative or positive is something you inherit from your parents, just like you inherit the color of your eyes or hair. Being Rh positive or negative does not affect your health.

While you are pregnant or delivering the baby, some of the baby's red blood cells may come in contact with your blood. If you are Rh negative and the baby has the Rh factor on his or her blood cells (Rh positive), your body will probably have a reaction to those cells and make antibodies to the Rh factor. This reaction is called sensitization. The antibodies may cross the placenta and destroy the red blood cells in your baby or any Rh-positive babies you have later. This destruction of red blood cells is called hemolytic disease. This disease can cause serious problems for the baby.

How does it occur?

Rh incompatibility happens only if you are Rh negative and your baby is Rh positive. It does not happen if you are Rh positive and your baby is Rh negative or if both of you are negative or positive.

Usually you are not exposed to a baby's blood until you give birth. This means that your first baby is not likely to be affected by the incompatibility. However, large amounts of the baby's blood often leak into the mother during delivery. Your body might then make antibodies. This can cause problems if you have another Rh-positive baby.

Sometimes a baby's blood may come in contact with your blood before delivery. This might happen, for example, if:

• You have a miscarriage with bleeding after 6 weeks of pregnancy.
• You terminate a pregnancy (also called a TOP or abortion).
• You have an ectopic pregnancy.
• The placenta breaks away from the uterus or is low in the uterus.

It may also happen after amniocentesis or other similar tests.

In most cases, development of antibodies can be prevented.

What are the symptoms?

You will have no symptoms. The baby will have symptoms if he or she develops hemolytic disease. The baby's red blood cells will start to break down silently, causing anemia. The anemia may cause yellow eyes and skin (jaundice), body swelling, and breathing problems, called hydrops or erythroblastosis fetalis. The baby might die in the womb if too much of the baby's blood is destroyed by the antibodies.

How is it diagnosed?

Blood tests are done to check for the Rh factor to see if you are Rh positive or negative. Blood tests also check for antibodies against the Rh factor. If you are Rh negative, the baby's father should also be tested. If the father's blood is Rh positive, the baby may inherit Rh-positive blood from him. If both you and the father are Rh negative, there will not be a problem because the baby will also be Rh negative.

Some of the tests used to check for hemolytic disease and its effects on the baby are:

• amniocentesis (a test of fluid around the baby)
• cordocentesis (removing blood from the baby's umbilical cord)
• ultrasound scan
• fetal blood flow evaluation of blood vessels in the baby's brain by Doppler ultrasound
• nonstress test (a check of the baby's activity and heart rate for a short time)
• blood tests
• biophysical profile (a check of the baby's movements, heart rate, and brain waves)

How is it treated?

If you have already been sensitized by a previous birth, your baby may have hemolytic disease before birth. In this case you may be referred to a maternal fetal medicine specialist (perinatologist) to help manage your pregnancy. Your baby will be carefully checked with ultrasound scans that look for signs of anemia. In some cases you may need an amniocentesis. These tests will help your provider know what treatment may be needed. For example, the baby may need a blood transfusion in the womb before birth. Sometimes early delivery by cesarean section (C-section) is necessary.

If you have not been sensitized, you will have a shot of Rh immune globulin (RhIg) at about 28 weeks of pregnancy. If you have not delivered the baby within 12 weeks of this first shot, you will have a second shot. You may also be given a shot within 72 hours after a birth (if the baby is Rh positive), miscarriage, termination of pregnancy, tubal (ectopic) pregnancy, or amniocentesis.

RhIg contains antibodies to the Rh factor. The antibodies in the shot will stop your body from making its own antibodies to the Rh factor. If you have the shot at 28 weeks and after delivery, sensitization will be prevented and Rh incompatibility should not be a problem during your next pregnancy.

If a mother is Rh negative, she should have the RhIg shot in all cases when the baby's blood could leak into her system. This includes:

• during or after all pregnancies, including ectopic pregnancies
• after early miscarriages or a termination of pregnancy
• after bleeding during the pregnancy
• after tests such as chorionic villus sampling or amniocentesis
• after external cephalic version (a procedure used to try to change a baby's position in the womb before birth)
• after injury to the abdomen
• after placenta abruption (when the placenta breaks away from the uterus)
• after placenta previa (when the placenta is placed low in the uterus)

If you have a threatened miscarriage but do not actually miscarry, you may also need a RhIg shot. Discuss this with your healthcare provider.

How long will the effects last?

Sensitization usually does not happen until after the birth of an Rh-positive baby. Therefore, in most cases Rh incompatibility is not a problem during your first pregnancy and delivery of an Rh-positive baby. However, later pregnancies and deliveries might be affected unless you are treated with RhIg.

Once you become sensitized, RhIg is not helpful. You will stay sensitized, and the effects are usually worse with each pregnancy.

What can be done to help prevent the problems of Rh incompatibility?

This problem of pregnancy has become much less common since doctors started using RhIg. RhIg can prevent sensitization. It is given to Rh-negative women right after every delivery, miscarriage, or termination of pregnancy. It is also given to pregnant Rh-negative women after amniocentesis, after any bleeding episodes, and during the 7th month of pregnancy.