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Rh Disease

 

 

Description of RH Disease

Rh disease of the newborn is caused by an incompatibility between the blood of a mother and her fetus. It is a hemolytic disease — that is, it causes destruction of fetal red blood cells. In the fetus or newborn, it can result in jaundice (yellowing of the skin and eyes), anemia, brain damage, heart failure and death. It does not affect the mother’s health.

Rh disease once affected 20,000 babies in the U.S. each year. Since 1968, how-ever, there has been a treatment that usually can prevent Rh disease. The number of babies born with the disease has declined dramatically since then. But not all women who need the treatment get it, and a small number of women cannot benefit from it. As a result, there are still some 4,000 infants born each year with Rh disease.

What Causes Rh Disease?

Most people have Rh-positive blood, meaning that they produce the Rh factor, an inherited protein found on the surface of their red blood cells. About 15 percent of the white population and 7 percent of the African-American population lack the Rh factor and are considered Rh-negative. The health of an Rh-negative person is not affected in any way. However, an Rh-negative woman is at risk of having a baby with Rh disease.

An Rh-negative mother and an Rh-positive father may conceive a baby who inherits the father’s Rh-positive blood. There is then a danger that, during pregnancy and especially during labor and delivery, some of the fetus’s Rh-positive red blood cells may get into the mother’s bloodstream. Since red blood cells containing the Rh factor are foreign to the mother’s system, her body tries to fight them off by producing antibodies against them. This triggering of the mother’s immune response is referred to as sensitization.

In a first pregnancy, there is very little danger to an Rh-positive fetus because the baby usually is born without sensitizing the mother, or at least before the mother produces substantial Rh antibodies. But, if sensitization occurs, in each later pregnancy maternal Rh antibodies can cross the placenta and reach the fetus. If the fetus has Rh-positive blood, the mother’s antibodies will destroy fetal blood cells. This results in Rh disease.

How Can Woman Find Out If She Is Rh-negative?

A simple blood test can tell if a woman is Rh-negative. This can be done in a health care provider’s office, clinic or hospital. Every woman should be tested early in pregnancy, or prior to pregnancy, to find out if she is Rh-negative.

How Can Rh Disease Be Prevented?

To prevent Rh disease, an Rh-negative woman should receive an injection of a blood product called Rh immunoglobulin (RhIg) within 72 hours of delivery of an Rh-positive baby. This will prevent sensitization in more than 95 percent of Rh-negative women. However, studies show that about 2 percent of pregnant women become sensitized prior to delivery. For this reason, an RhIg injection is given at about 28 weeks of pregnancy, as well as after delivery.

RhIg also should be given to an Rh-negative woman after a miscarriage, an ectopic pregnancy, an induced abortion, or a blood transfusion with Rh-positive blood. Treatment also is recommended after amniocentesis (a procedure used to obtain a small sample of amniotic fluid), and after another prenatal test called chorionic villus sampling (CVS).

How Does RhIg Work?

RhIg contains antibodies to the Rh factor. The antibodies quickly attach to and help destroy any Rh-positive fetal cells in the mother’s bloodstream. As a result, the mother’s body does not produce any antibodies against the Rh-positive fetal cells.

Protection by RhIg lasts only about 12 weeks, so treatment must be repeated with each pregnancy, and with the situations cited above in which fetal blood cells can mix with the mother’s blood.

Does RhIg Treatment Always Work?

RhIg will not work for an Rh-negative woman who is already sensitized (that is, her body has produced its own antibodies to Rh-positive cells) due to a prior pregnancy, miscarriage, abortion or transfusion. A blood test can determine whether an Rh-negative woman has been sensitized.

Is There Any Way To Get Rid of the Mother's Antibodies?

No. Although a woman will have no symptoms and stay as healthy as ever, she can continue to produce antibodies as part of her blood. If she has any more Rh-positive babies, they could develop Rh disease.

How Is Rh Disease Treated Before Birth?

When a mother already has antibodies, the baby’s father also should be tested. If he is Rh-negative, the baby also will be Rh-negative (so the fetus is not at risk of Rh disease), and the pregnant woman will not require further testing. If the father is Rh-positive (or if his Rh status is not known), doctors now offer sensitized pregnant women amniocentesis, in which a needle is inserted into a woman’s abdomen to withdraw a small amount of amniotic fluid in order to determine whether the fetus is Rh-positive or Rh-negative. (An experimental maternal blood test also is showing promise in determining fetal Rh status, and may eventually reduce the need for amniocentesis, which poses a very small risk of miscarriage.) If the fetus is Rh-positive, or if it is not known whether the fetus is Rh-positive or Rh-negative, the health care provider will measure the levels of antibodies in the mother’s blood as pregnancy progresses. If high levels of antibodies are found, special tests will be recommended that can help determine if the baby is developing Rh disease.

Amniocentesis can show whether the fetus is severely affected by the mother’s antibodies. Ultrasound examination also can help determine the condition of the fetus.

Based on the results of these and other tests, the health care provider may advise inducing labor early, before the mother’s antibodies destroy too many fetal blood cells. After delivery, if the baby is anemic or very jaundiced, a blood transfusion may be necessary. Mild jaundice may be treated by placing the baby under special blue lights (phototherapy). Some mild cases do not need any treatment.

In recent years, there has been great progress in treating fetuses who have severe Rh disease. These fetuses, who are at high risk of death, may be treated with blood transfusions as early as the 18th week of pregnancy so that, today, more than 90 percent of treated babies with severe disease survive.

The development of a technique called cordocentesis in the 1980s represented a major advance in the treatment of Rh disease. Guided by ultrasound, the doctor threads a thin needle through a mother’s abdomen into a tiny blood vessel in the umbilical cord and injects the blood transfusion. Cordocentesis also is used to determine the degree of fetal blood cell destruction, letting doctors know if the fetus needs immediate transfusion and how much blood is needed.

What Happens If Both a Mother and Her Fetus Are Rh-negative?

If both the mother and the father are Rh-negative, the baby will be Rh-negative as well. In this case, the baby is not at risk of developing Rh disease. The mother will not require treatment with RhIg following delivery.

Even if the father is Rh-positive, he may carry an Rh-negative gene, which the baby has a 50 percent chance of inheriting. Since there currently is no entirely safe way to learn the fetus’s Rh type, a pregnant woman who is Rh-negative should be treated with RhIg at 28 weeks of pregnancy, even though the baby may be found to be Rh-negative at birth. Of course, if the baby is found to be Rh-positive, RhIg also is given following delivery.

Can the RhIg Treatment Transmit the AIDS Virus?

Although RhIg is a blood product, it appears completely safe. The donated blood, which has been screened for the AIDS virus, is treated with a substance that kills viruses and bacteria. There have been no cases of AIDS associated with use of RhIg, nor has it been shown to transmit hepatitis or any other infectious diseases.

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