Condition Basics

What is Rh sensitization during pregnancy?

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 during pregnancy doesn't cause any warning symptoms. A blood test is the only way to know you have it or are at risk for it.

What causes Rh sensitization, and what problems does it cause?

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.

Who gets Rh sensitization?

Rh sensitization during pregnancy can only happen if the mother has Rh-negative blood and the baby has Rh-positive blood.

• 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. Rh 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.

If you have Rh-negative blood, your doctor will probably treat you as though the baby's blood is Rh-positive no matter what the father's blood type is. This is just to be extra safe.

How is it diagnosed?

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.

How is it prevented?

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.

How is Rh sensitization treated?

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.