Positive News for Rh Negative Women

Q: I am a 21-year-old woman, and I am planning to get pregnant. Three years ago, I was told that I was Rh negative and that when I become pregnant, I have the chance of dying, along with my baby. I have asked doctors before and feel that I have never gotten a straight answer. If you have any information on this topic, I would love to hear it.

A: Your situation is not that unusual, and it's not as risky as you may think. About one in seven women in the United States is Rh-negative. Their pregnancies are usually uneventful and the vast majority will deliver healthy babies. Most importantly, your Rh status does not increase your risk of dying in pregnancy.

We all have several different markers, called antigens, in our red blood cells. The bodies of people who don't have certain antigens often make antibodies, or large molecules that can attack and destroy antigens that are foreign to them. (The fact that we make antibodies to attack foreign material in our bodies is the basis of an important science called immunology.)

One of the antigens in our red blood cells is the Rh factor. People who carry the Rh factor are Rh-positive, and people who do not carry it are Rh-negative. In the United States, about 85 percent of the population is Rh positive and 15 Rh-negative.

People who are Rh negative and are exposed to Rh positive red cells can become sensitized and start making antibodies that attack and destroy the Rh positive cells which are foreign to them.

Sensitization can happen, for example, if someone receives the wrong kind of blood in transfusion. The chance of receiving the wrong blood type is remote, because blood banks are very careful in matching the blood types.

During a normal pregnancy, an Rh-negative mother can become sensitized at any time, because the fetal red cells regularly enter her circulation. An Rh-negative pregnant woman also is at risk of becoming sensitized:

• At the time of delivery
• During bleeding episodes in pregnancy such as abruptio placentae or placenta previa
• During invasive procedures such as amniocentesis, or cordocentesis
• If she has an ectopic pregnancy
• If she has a miscarriage

Rh-sensitization doesn't usually create a problem in a first pregnancy. (And if both parents are Rh-negative, a baby is always Rh negative and cannot sensitize the mother.)

But if a Rh-negative woman who has been exposed to Rh positive cells in her first pregnancy gets pregnant again, her body "remembers," and starts producing antibodies when exposed again to Rh-positive cells. These antibodies can cross the placenta and attack the fetus' red cells, often leading to destruction of the cells and subsequent fetal anemia. As a result the fetal heart may not be able to keep up with the blood volume, and the fetus can develop heart failure and accumulate excess fluid in its body.

In the past, Rh sensitization, or erythroblastosis fetalis, was a major problem, injuring and killing many babies. Fortunately, these days Rh sensitization can be prevented. During the first prenatal visit, every women has a Coombs test to check the blood for the presence of antibodies. Rh-negative women have this test done several times during pregnancy to make sure they don't become sensitized.

To prevent sensitization, Rh-negative pregnant women are given intramuscular injections of a medicine called Rh immunoglobulin (RhIg) at 28 weeks and after delivery. RhIg stays in the blood system for up to three months and prevents the body from recognizing Rh-positive cells as foreign bodies. RhIg is also given at other times when the mother is at increased risk of being exposed to the baby's cells, as noted in the list above.

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