What is rh sensitization?

Unless you are given Rh immune globulin just before or after a high–risk event, you have a chance of becoming sensitized to an Rh–positive fetus's blood. High-risk events include miscarriage, amniocentesis, abortion, ectopic pregnancy, and childbirth.

If you have been Rh-sensitized in the past

If you have been Rh–sensitized in the past, you must be closely watched during any pregnancy with an Rh–positive partner. That's because your baby (fetus) is more likely to have Rh–positive blood. If your baby is Rh–positive, your immune system may quickly develop IgG antibodies. They can cross the placenta and cause fetal red blood cells to be destroyed. Each later pregnancy with an Rh–positive fetus may cause more serious problems for the fetus. Your unborn baby could get a disease called Rh disease, which can be mild to severe. This is also called hemolytic disease of the newborn, or erythroblastosis fetalis.

• Mild Rh disease means there's limited destruction of fetal red blood cells. It could cause mild fetal anemia. The baby can usually be carried to term and needs no special treatment. The baby might have problems with jaundice after birth. Mild Rh disease is more likely to develop in the first pregnancy after sensitization has occurred.
• Moderate Rh disease means that larger numbers of fetal red blood cells are destroyed. The fetus may get an enlarged liver and may become somewhat anemic. The baby may need to be delivered before your due date. And the baby may need a blood transfusion before (while in the uterus) or after birth. A newborn with moderate Rh disease is watched closely for jaundice.
• Severe Rh disease (fetal hydrops) means there's widespread destruction of fetal red blood cells. The fetus develops severe anemia, liver and spleen enlargement, high bilirubin levels, and fluid retention (edema). The fetus may need one or more blood transfusions before birth. A fetus with severe Rh disease who survives the pregnancy may need a blood exchange. It replaces most of the infant's blood with donor blood. (The blood is usually type O, Rh-negative.)
• If you've already had a pregnancy with Rh disease, it's a sign that you will need special treatment when you are pregnant with an Rh–positive fetus.

If you are Rh-sensitized and your baby is at risk for Rh disease, your doctor will watch your pregnancy closely. You may have:

• Regular blood tests. These check the level of antibodies in your blood.
• A Doppler ultrasound. This checks the blood flow to your baby's brain. It can show anemia and how severe it is.
• Amniocentesis after 15 weeks. This checks your baby's blood type and Rh factor and looks for problems.

If you are already Rh-sensitized or you become Rh-sensitized while pregnant, you won't have any unusual symptoms. Fetal problems from Rh sensitization are found with Doppler ultrasound testing and sometimes with amniocentesis. A fetus with severe Rh disease may move less often than he or she did earlier in the pregnancy.

Treatment options depend on how well or poorly the baby is doing. Treatment focuses on preventing or reducing fetal harm and on avoiding early (preterm) delivery.

Treatment is based on how severe the loss of red blood cells (anemia) is.

• If the baby's anemia is mild, you will just have more testing than usual while you are pregnant. The baby may not need any special treatment after birth.
• If anemia is getting worse, it may be safest to deliver the baby early. After delivery, some babies need a blood transfusion or treatment for jaundice.
• For severe anemia, a baby can have a blood transfusion while still in the uterus. This can help keep the baby healthy until he or she is mature enough to be delivered. You may have an early C-section, and the baby may need to have another blood transfusion right after birth.

An intrauterine fetal blood transfusion is sometimes used to supply healthy blood to a fetus with severe hemolytic disease of the newborn (also called Rh disease or erythroblastosis fetalis). Blood is given to the fetus before it is born, usually through the vein or artery in the umbilical cord. This replaces the red blood cells that are being destroyed by the Rh-sensitized mother's immune system.

A blood transfusion or exchange transfusion is sometimes given to a newborn to treat severe anemia or jaundice related to Rh disease.

If you have Rh-negative blood but aren't Rh-sensitized, you may need one or more shots of Rh immune globulin (such as RhoGAM). This prevents Rh sensitization in nearly all women who use it. The shots only work for a short time, so you'll need shots each time you get pregnant.

Anyone who is pregnant will get a blood test at their first prenatal visit to see what their blood type is. If your blood is Rh-negative, it will also be tested for antibodies to Rh-positive blood. This is done with an Rh antibodies screening test or indirect Coombs test. If you have antibodies, it means that you have been sensitized to Rh-positive blood.

If you have Rh-negative blood and are not Rh-sensitized, you will have this test again later in pregnancy.

• The blood test may be repeated between 24 and 28 weeks of pregnancy. If the test still shows that you aren't sensitized, you probably won't need another antibody test until delivery.
• Your baby will have a blood test at birth. If the newborn has Rh-positive blood, you will have an antibody test to see if you were sensitized during late pregnancy or childbirth.

A woman who may have problems with Rh incompatibility or sensitization can be treated by:

• A family medicine physician, for mild fetal Rh disease.
• An obstetrician, for mild to moderate Rh disease.
• A perinatologist, for moderate to severe fetal Rh disease (hydrops).

If you test positive for Rh sensitization, your health care system or health professional may want you to be followed and treated by a perinatologist or an obstetrician who can easily call in a perinatologist.

If the mother is Rh-negative and the father is Rh-positive, there's a good chance that the baby will have Rh-positive blood. Sensitization can occur. If both parents have Rh-negative blood, the baby will have Rh-negative blood. Since the mother's blood and the baby's blood match, sensitization won't occur.

You may have Rh-negative blood, and your baby may have Rh-positive blood. If the two types of blood mix, your body will make antibodies. This is called Rh sensitization. In most cases, this isn't a problem the first time you're pregnant. But in future pregnancies, sensitization could cause problems.

Rh sensitization can occur during pregnancy if you are Rh-negative and pregnant with a developing baby who has Rh-positive blood. If your blood mixes with the Rh-positive blood of your baby, you can develop antibodies against your baby's blood. It happens because Rh-negative blood cells don't have a marker called Rh factor on them, but Rh-positive blood cells do.

In most cases, your blood will not mix with your baby's blood until delivery. It takes a while to make antibodies that can affect the baby. So during your first pregnancy, the baby probably would not be affected.

But if you get pregnant again, the antibodies could attack your baby's red blood cells. This can cause the baby to have anemia, jaundice, or more serious problems (Rh disease). The problems will tend to get worse with each Rh-positive pregnancy you have.