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. Without treatment, the most severely affected fetuses are stillborn. In the newborn, Rh disease 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 about 20,000 babies in the U.S. each year. Since 1968, however, 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, only 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 type. 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 before the mother is sensitized, or at least before the mother produces substantial Rh antibodies. But, if sensitization occurs, the woman will continue to produce antibodies as part of her blood throughout her life. In each later pregnancy, maternal Rh antibodies can cross the placenta and reach the fetus. Each subsequent baby becomes at greater risk for more severe Rh disease. If the fetus has Rh-positive blood, the mother’s antibodies will destroy fetal blood cells. This results in Rh disease for the baby.

How can a 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, all babies of an Rh-negative woman should be tested for their Rh type by a simple blood test at birth. All Rh-negative mothers of Rh-positive babies should receive an injection of a purified blood product called Rh immune globulin (RhIg) within 72 hours of delivery. 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 blood cells because these cells are removed from the mother’s blood before her body responds to them.

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 already is 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 the doctor does not do amniocentesis and so does not know if 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.

These tests may include amniocentesis and cordocentesis, in which the doctor inserts a thin needle through the mother’s abdomen, guided by ultrasound, into a tiny blood vessel in the umbilical cord to take a blood sample from the fetus. These tests help determine whether the baby is developing anemia and how severe it may be. Both tests, which often need to be repeated every 2 to 4 weeks, pose a small risk of miscarriage. A recent study reported that an ultrasound examination that measures the speed of blood flowing through an artery in the fetus’s head was accurate in detecting moderate to severe anemia (which would require prenatal treatment), but not mild anemia (which often does not require treatment). If this ultrasound test, which poses no risk to the fetus, proves to be accurate, it eventually may reduce the need for amniocentesis and cordocentesis to monitor fetuses at risk of Rh disease.

Based upon 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 has jaundice, he may be placed under special blue lights (phototherapy). When jaundice does not respond to phototherapy, or when the baby is anemic, a blood transfusion may be necessary. Some cases of Rh disease are so mild that they require no treatment.

In recent years, there has been great progress in treating fetuses who have severe Rh disease. The development of cordocentesis in the 1980s represented a major advance in the treatment of Rh disease. Severely affected fetuses, who are at high risk of death, can be treated with blood transfusions, usually using cordocentesis, as early as the 18th week of pregnancy. Today, more than 90 percent of treated babies with severe Rh disease survive.

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 (so each fetus would have a 50:50 chance of being Rh-negative). 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 almost completely safe. The donated blood, which has been screened for the AIDS and hepatitis viruses, is treated with a substance that kills viruses and bacteria. Even with widespread use, there have been no cases of AIDS associated with use of RhIg. There has only been a single report of hepatitis from RhIg, occurring from a product produced in 1978 before the current hepatitis screening was available.