Rh Incompatibility
What is Rh incompatibility?
Having Rh incompatibility when you are pregnant means that 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.
You have probably heard that your blood type is A, B, AB, or O, and positive or negative. For example, your blood type might be A positive or A negative. The positive or negative part of the blood type refers to your blood’s Rh factor.
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 usually 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 is Rh positive, your body will probably have a reaction to the baby’s red blood cells. Your body will make antibodies to the Rh factor. This reaction is called sensitization. The antibodies could cross the placenta and destroy the red blood cells in your baby. This could also happen with Rh-positive babies you have after this baby. The destruction of red blood cells is called hemolytic disease. This disease can cause serious problems for the baby.
What is the cause?
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. It also does not happen if both of you are negative or both of you are 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 your body during delivery. Your body might then make antibodies to the Rh factor. This can cause problems if you have another Rh-positive baby.
Sometimes a baby's blood can come into 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 (abortion).
- You have a tubal pregnancy.
- The placenta breaks away from the uterus or is low in the uterus.
It may also happen after amniocentesis or other similar tests.
What are the symptoms?
You will not have any symptoms. The baby will have symptoms if he or she has hemolytic disease. The baby's red blood cells will start to break down, causing anemia. The anemia may cause yellow eyes and skin (jaundice), swelling, and breathing problems. 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 can show 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 of the baby
- a check of blood flow in the baby’s brain with ultrasound
- nonstress test (a monitor test to check the baby's activity and heart rate for a short time)
- blood tests
How is it treated?
If you have not yet been sensitized, shots of Rh immune globulin (RhIg) can stop your body from making antibodies to the Rh factor. 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 are Rh negative, you may be given a shot of RhIg at about 28 weeks of pregnancy. If the baby has not yet been born 12 weeks later, 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).
The RhIg shots should prevent sensitization, and Rh incompatibility should not be a problem during your next pregnancy.
If you are Rh negative, you should have the RhIg shot in all cases when the baby's blood could leak into your system. This includes:
- during or after all pregnancies, including tubal pregnancies
- after a miscarriage or abortion
- after bleeding during the pregnancy
- after tests such as chorionic villus sampling or amniocentesis
- after external cephalic version (a procedure done to change a baby's position before birth)
- after injury to the belly
- after problems with the placenta, such as placenta abruption or placenta previa
If you have a threatened miscarriage but do not actually miscarry, you may also need a RhIg shot. Discuss this with your healthcare provider.
If you have been sensitized by a previous birth, your baby may have hemolytic disease before birth. In this case you may be referred to a specialist called a perinatologist to help manage your pregnancy. Your baby will be carefully checked with ultrasound scans that look for signs of anemia. In some cases fluid in the amniotic sac may be checked with amniocentesis. The 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 the baby needs to be delivered early with a C-section.
How long will the effects last?
Your body usually does not start making antibodies to the Rh factor until after the birth of an Rh-positive baby. This means that Rh incompatibility is usually not a problem with your first Rh-positive baby. However, later pregnancies and deliveries might be affected unless you are treated with the RhIg shot.
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 pregnancy problem has become much less common since healthcare providers started using RhIg to prevent sensitization.
