Rh Sensitization During Pregnancy

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Topic Overview

What is Rh sensitization during pregnancy?

If your blood is Rh-negative and your unborn baby’s blood is Rh-positive, your body’s natural defense system can make your unborn baby (fetus) sick. This happens because your body makes a substance that can destroy the baby’s red blood cells. This reaction is called Rh sensitization.

Rh sensitization can only happen to women with Rh-negative blood. You cannot become Rh-sensitized if your blood is Rh-positive.

This condition does not happen often and can almost always be prevented. It is one reason why you need to see your doctor regularly when you are pregnant.

What causes Rh sensitization during pregnancy?

Rh sensitization happens when the mother’s Rh-negative blood mixes with the baby’s Rh-positive blood. For most women, this happens during childbirth. It may also happen during a miscarriage or abortion, or in women who share needles to take illegal drugs.

If you are pregnant and have Rh-negative blood, and the father of the baby has Rh-positive blood, your fetus could have Rh-positive blood.

If both you and the baby’s father have Rh-negative blood, your baby will be Rh-negative. In this case, there is no chance of Rh sensitization.

Does Rh sensitization in the mother harm the fetus?

Rh sensitization usually does not hurt your unborn baby (fetus) the first time you are pregnant. But in your next pregnancy, it can make your fetus sick. The fetus can develop anemia, also known as hemolytic disease of the fetus and newborn. If untreated, sensitization can cause severe swelling of the fetus's body (hydrops fetalis). In rare cases, the fetus may die.

What are the symptoms of Rh sensitization?

You will not have any unusual symptoms when you are Rh sensitive, so your doctor will closely watch your pregnancy. Regular blood tests can help your doctor watch the health and growth of your fetus.

As the pregnancy progresses, a fetus with severe Rh disease may move less often than before.

How is Rh sensitization diagnosed?

A simple blood test can check for Rh incompatibility. This is usually done at the first visit early in your pregnancy, before the 12th week.

If this test shows that your blood is Rh-negative, your doctor will know to watch your pregnancy carefully. You will also have a blood test to see if you are already Rh-sensitized.

If the test shows that you are not Rh-sensitized, you may have another test between your 24th and 28th weeks of pregnancy. If that test also shows that you are not sensitized, you will not have more Rh tests until delivery unless you get another problem, such as placenta abruptio.

If your newborn is Rh-positive, you will have more blood tests to find out if you were sensitized in late pregnancy or childbirth.

If your first blood test shows that you are Rh-sensitized (or if you become sensitized during this pregnancy), your doctor will watch closely to see if your fetus is being harmed. This will include regular blood tests and other tests.

How is Rh sensitization treated?

A shot of medicine called immune globulin can greatly lower your chances of Rh sensitization. You must get the shot around week 28 of your pregnancy to prevent sensitization late in your pregnancy or during delivery. If your baby is Rh-positive at birth, you will have another shot of Rh immune globulin after delivery.

For pregnant women who are already Rh-sensitized from a past pregnancy, Rh immune globulin cannot help. Instead, the goal of treatment is to prevent or reduce harm to the fetus and prevent early (preterm) delivery. Treatment choices depend on how badly your fetus may be harmed by the Rh sensitization.

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Last updated:	November 10, 2005
Author:	Kathe Gallagher, MSW
Reviewed By:	Patrice Burgess, MD - Family Medicine, Kirtly Jones, MD - Obstetrics and Gynecology
Editors:	Kathleen M. Ariss, MS, Lisa Shaw