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Rh Sensitization During Pregnancy


Topic Overview

What is Rh sensitization during pregnancy?

If you are Rh-negative, your red blood cells do not have a marker called Rh factor on them. Rh-positive blood does have this marker. If your blood mixes with Rh-positive blood, your immune system will react to the Rh factor by making antibodies to destroy it. This immune system response is called Rh sensitization.

What causes Rh sensitization during pregnancy?

Rh sensitization can occur during pregnancy if you are Rh-negative and pregnant with a developing baby (fetus) who has Rh-positive blood. 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 with an Rh-positive baby, the antibodies already in your blood could attack the baby's red blood cells. This can cause the baby to have anemia, jaundice, or more serious problems. This is called Rh disease. The problems will tend to get worse with each Rh-positive pregnancy you have.

Rh sensitization is one reason it's important to see your doctor in the first trimester of pregnancy. It doesn't cause any warning symptoms, and a blood test is the only way to know you have it or are at risk for it.

  • If you are at risk, Rh sensitization can almost always be prevented.
  • If you are already sensitized, treatment can help protect your baby.

Who gets Rh sensitization during pregnancy?

Rh sensitization during pregnancy can only happen if a woman has Rh-negative blood and only if her baby has Rh-positive blood.

  • If the mother is Rh-negative and the father is Rh-positive, there is a good chance 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 will not 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, just to be on the safe side.

How is Rh sensitization diagnosed?

All pregnant women get a blood test at their first prenatal visit during early pregnancy. This test will show if you have Rh-negative blood and if you are Rh-sensitized.

If you have Rh-negative blood but are not sensitized:

  • The blood test may be repeated between 24 and 28 weeks of pregnancy. If the test still shows that you are not sensitized, you probably will not need another antibody test until delivery. (You might need to have the test again if you have an amniocentesis, if your pregnancy goes beyond 40 weeks, or if you have a problem such as placenta abruptio, which could cause bleeding in the uterus.)
  • 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.

If you are Rh-sensitized, your doctor will watch your pregnancy carefully. You may have:

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

How is Rh sensitization prevented?

If you have Rh-negative blood but are not Rh-sensitized, your doctor will give you one or more shots of Rh immune globulin (such as RhoGAM). This prevents Rh sensitization in about 99 women out of 100 who use it.1

You may get a shot of Rh immune globulin:

  • If you have a test such as an amniocentesis.
  • Around week 28 of your pregnancy.
  • After delivery if your newborn is Rh-positive.

The shots only work for a short time, so you will need to repeat this treatment each time you get pregnant. (To prevent sensitization in future pregnancies, Rh immune globulin is also given when an Rh-negative woman has a miscarriage, abortion, or ectopic pregnancy.)

The shots won't work if you are already Rh-sensitized.

How is it treated?

If you are Rh-sensitized, you will have regular testing to see how your baby is doing. You may also need to see a doctor who specializes in high-risk pregnancies (a perinatologist).

Treatment of the baby 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 will most likely have an early C-section, and the baby may need to have another blood transfusion right after birth.

In the past, Rh sensitization was often deadly for the baby. But improved testing and treatment mean that now most babies with Rh disease survive and do well after birth.

Frequently Asked Questions

Learning about Rh sensitization during pregnancy:

Being diagnosed:

Getting treatment:

Ongoing concerns:

Living with Rh sensitization:

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