What Is Rh Incompatibility?

Rh incompatibility is a condition that occurs during pregnancy if a woman has Rh-negative blood and her baby has Rh-positive blood.

"Rh-negative" and "Rh-positive" refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells. If you have Rh factor, you're Rh-positive. If you don't have it, you're Rh-negative. Rh factor is inherited (passed from parents to children through the genes). Most people are Rh-positive.

Whether you have Rh factor doesn't affect your general health. However, it can cause problems during pregnancy.

Overview

When you're pregnant—especially during delivery—blood from your baby can cross into your bloodstream. If you're Rh-negative and your baby is Rh-positive, your body will react to the baby's blood as a foreign substance.

Your body will create antibodies (proteins) against the baby's Rh-positive blood. These antibodies usually don't cause problems during a first pregnancy. This is because the baby often is born before many of the antibodies develop.

However, the antibodies stay in your body once they have formed. Thus, Rh incompatibility is more likely to cause problems in second or later pregnancies (if the baby is Rh-positive).

The Rh antibodies can cross the placenta and attack the baby's red blood cells. This can lead to hemolytic anemia (HEE-moh-lit-ick uh-NEE-me-uh) in the baby.

Hemolytic anemia is a condition in which red blood cells are destroyed faster than the body can replace them. Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, your baby won't get enough oxygen. This can lead to serious problems. Severe hemolytic anemia may even be fatal to the child.

Outlook

With prompt and proper prenatal care and screening, you can prevent the problems of Rh incompatibility. Screening tests will allow your doctor to find out early in your pregnancy whether you're at risk for this condition.

If you're at risk, your doctor will carefully check on you and your baby throughout your pregnancy and prescribe treatment as needed.

Injections of a medicine called Rh immune globulin can keep your body from making Rh antibodies. This medicine helps prevent the problems of Rh incompatibility. If you're Rh-negative, you'll need this medicine every time you have a baby with Rh-positive blood.

Other events also can expose you to Rh-positive blood, which could affect a pregnancy. Examples include a miscarriage or blood transfusion. If you're treated with Rh immune globulin right after these events, you may be able to avoid Rh incompatibility during your next pregnancy.

Other Names for Rh Incompatibility

• Rh disease
• Rh-induced hemolytic disease of the newborn

What Causes Rh Incompatibility?

A difference in blood type between a pregnant woman and her baby causes Rh incompatibility. The condition occurs if a woman is Rh-negative and her baby is Rh-positive.

When you're pregnant—especially during delivery—blood from your baby can cross into your bloodstream. If you're Rh-negative and your baby is Rh-positive, your body will react to the baby's blood as a foreign substance.

Your body will create antibodies (proteins) against the baby's Rh-positive blood. These antibodies can cross the placenta and attack the baby's red blood cells. This can lead to hemolytic anemia in the baby.

Rh incompatibility usually doesn't cause problems with a first pregnancy. The baby often is born before many of the antibodies develop.

The condition is more likely to cause problems in second or later pregnancies (if the baby is Rh-positive). Once you've formed Rh antibodies against the Rh-positive red blood cells, the antibodies remain in your body.

With each pregnancy that follows, your body continues to make Rh antibodies. As a result, each Rh-positive baby you conceive becomes more at risk for serious problems, such as severe hemolytic anemia.

Who Is At Risk for Rh Incompatibility?

An Rh-negative woman who conceives a child with an Rh-positive man is at risk for Rh incompatibility.

Rh factor is inherited (passed from parents to children through the genes). If you're Rh-negative and the father of your baby is Rh-positive, there's a 50 percent or more chance that the baby will have Rh-positive blood.

Simple blood tests can show whether you and the father of your baby are Rh-positive or Rh-negative.

If you're Rh-negative, your risk for problems from Rh incompatibility is higher if you were exposed to Rh-positive blood before the pregnancy. This may have happened during:

• An earlier pregnancy (usually during delivery)
• A miscarriage
• An induced abortion
• A blood transfusion
• Bleeding during pregnancy

Certain tests also can expose you to Rh-positive blood. Examples include amniocentesis (AM-ne-o-sen-TE-sis) and chorionic villus (ko-re-ON-ik VIL-us) sampling (CVS).

Amniocentesis is a test that may be done during pregnancy. Your doctor uses a needle to remove a small amount of fluid from the sac around your baby. The fluid is then tested for various reasons.

CVS also may be done during pregnancy. For this test, your doctor threads a thin tube through the vagina and cervix to the placenta. He or she removes a tissue sample from the placenta using gentle suction. The tissue sample is tested for various reasons.

Unless you were treated with the medicine that prevents Rh antibodies (Rh immune globulin) after each of these events, you're at risk for Rh incompatibility during current and future pregnancies.

What Are the Signs and Symptoms of Rh Incompatibility?

Rh incompatibility doesn't cause signs or symptoms in a pregnant woman. In a baby, the condition can lead to hemolytic anemia.

Hemolytic anemia is a condition in which red blood cells are destroyed faster than the body can replace them. Red blood cells contain hemoglobin (HEE-muh-glow-bin), an iron-rich protein that carries oxygen to your body.

Without enough red blood cells and hemoglobin, the blood can't carry enough oxygen to the body.

Hemolytic anemia can cause mild to severe signs and symptoms in a newborn, such as jaundice and a buildup of fluid.

Jaundice is a yellowish color of the skin or whites of the eyes. When red blood cells die, they release hemoglobin into the blood. The hemoglobin is broken down into a compound called bilirubin, which gives the skin and eyes a yellowish color. High levels of bilirubin can lead to brain damage in the baby.

The buildup of fluid is a result of heart failure. Without enough hemoglobin-carrying red blood cells, the heart has to work harder to move oxygen-rich blood through the body. This stress can lead to heart failure. Heart failure can cause fluid to build up in various parts of the body. When this occurs in a fetus or newborn, the condition is called hydrops fetalis.

Severe hemolytic anemia can be fatal to a newborn at the time of birth or shortly after.

How Is Rh Incompatibility Diagnosed?

Rh incompatibility is diagnosed with blood tests. To find out whether a baby is developing hemolytic anemia and how serious it is, doctors may use more advanced tests, such as ultrasound.

Specialists Involved

An obstetrician will screen for Rh incompatibility. This is a doctor who specializes in treating pregnant women. The obstetrician also will monitor the pregnancy and the baby for problems related to hemolytic anemia. He or she also will oversee treatment to prevent problems with future pregnancies.

A pediatrician or hematologist treats newborns for hemolytic anemia and related problems. A pediatrician is a doctor who specializes in treating children. A hematologist is a doctor who specializes in treating blood diseases and disorders.

Diagnostic Tests

If you're pregnant, your doctor will order a simple blood test at your first prenatal visit to learn whether you're Rh-positive or Rh-negative.

If you're Rh-negative, you also may have another blood test called an antibody screen. This test shows whether you have Rh antibodies in your blood. If you do, it means that you were exposed to Rh-positive blood before and you're at risk for Rh incompatibility.

If you're Rh-negative and you don't have Rh antibodies, your baby's father also will be tested to find out his Rh type. If he's Rh-negative like you, there's no chance that the baby has Rh-positive blood. Thus, there's no risk of Rh incompatibility.

However, if the baby's father is Rh-positive, there's a 50 percent or more chance that the baby has Rh-positive blood. As a result, you're at high risk of developing Rh incompatibility.

If your baby's father is Rh-positive, or if his Rh status can't be determined, your doctor may do a test called amniocentesis. For this test, your doctor inserts a hollow needle through your abdominal wall into your uterus. He or she removes a small amount of fluid from the sac around the baby. The fluid is tested to learn whether the baby is Rh-positive.

Your doctor also may use this test to measure bilirubin levels in your baby. Bilirubin builds up as a result of red blood cells dying too quickly. The higher the level of bilirubin is, the greater the baby's chances for hemolytic anemia.

If Rh incompatibility is known or suspected, you'll be tested for Rh antibodies one or more times during your pregnancy. This test often is done at least once at your sixth or seventh month of pregnancy.

The results from this test also can suggest how severe the baby's hemolytic anemia has become. Higher levels of antibodies suggest more severe hemolytic anemia.

To check your baby for hemolytic anemia, your doctor also may use Doppler ultrasound. He or she will use this test to measure how fast blood is flowing through an artery in the baby's head.

Doppler ultrasound uses sound waves to measure how fast blood is moving. The faster the blood flow is, the greater the chances for hemolytic anemia. This is because the anemia will cause the baby's heart to pump more blood.

How Is Rh Incompatibility Treated?

Rh incompatibility is treated with a medicine called Rh immune globulin.

Treatment for a baby who has hemolytic anemia will vary depending on how severe the condition is.

Goals of Treatment

The goals of treating Rh incompatibility are to ensure that your baby is healthy and to lower your risk for the condition in future pregnancies.

Treatment for Rh Incompatibility

If Rh incompatibility is diagnosed during your pregnancy, you'll receive Rh immune globulin in your seventh month of pregnancy and again within 72 hours of delivery.

Rh immune globulin contains Rh antibodies that attach to the Rh-positive blood cells in your blood. When this happens, your body doesn't react to the baby's Rh-positive cells as a foreign substance. As a result, your body doesn't make Rh antibodies. Rh immune globulin must be given at the correct times to work properly.

Once you have formed Rh antibodies, the medicine will no longer help. That's why a woman who has Rh-negative blood must be treated with the medicine with each pregnancy or any other event that allows her blood to mix with Rh-positive blood.

Rh immune globulin is injected into the muscle of your arm or buttock. Side effects may include soreness at the injection site and a slight fever.

Treatment for Hemolytic Anemia

Several options are available for treating hemolytic anemia in a baby. In mild cases, no treatment may be needed. In more serious cases, the baby may get a blood transfusion through the umbilical cord.

If hemolytic anemia is severe and the baby is almost full-term, your doctor may induce labor early. This allows the baby's doctor to begin treatment right away.

A newborn who has severe anemia may be treated with a blood exchange transfusion. The procedure involves slowly removing the newborn's blood and replacing it with fresh blood or plasma from a donor.

Newborns also may be treated with special lights to reduce the amount of bilirubin in their blood. These babies may have jaundice (a yellowish color of the skin or whites of the eyes). High levels of bilirubin cause jaundice.

Reducing the blood's bilirubin level is important because high levels of this compound can cause brain damage. High levels of bilirubin often are seen in babies who have hemolytic anemia. This is because the compound forms when red blood cells break down.

How Can Rh Incompatibility Be Prevented?

Rh incompatibility can be prevented with Rh immune globulin, as long as the medicine is given at the correct times. Once you have formed Rh antibodies, the medicine will no longer help.

That's why a woman who has Rh-negative blood must be treated with Rh immune globulin during and after each pregnancy or after any other event that allows her blood to mix with Rh-positive blood.

Early prenatal care also can help prevent some of the problems linked to Rh incompatibility. Early prenatal care allows your doctor to find out early whether you're at risk for the condition.

If you're at risk, your doctor can closely monitor your pregnancy and watch for signs of hemolytic anemia in your baby. He or she can treat the baby as needed to increase your chances of having a healthy baby.

Living With Rh Incompatibility

If you have Rh-negative blood, injections of Rh immune globulin can reduce your risk for Rh incompatibility in future pregnancies. It's important to get this medicine every time you give birth to an Rh-positive baby or come in contact with Rh-positive blood.

If you're Rh-negative, your risk for problems from Rh incompatibility is higher if you were exposed to Rh-positive blood before your current pregnancy. This may have happened during:

• An earlier pregnancy (usually during delivery)
• A miscarriage
• An induced abortion
• A blood transfusion
• Bleeding during pregnancy

You also can be exposed to Rh-positive blood during certain tests, such as amniocentesis and chorionic villus sampling. (For more information, see "Who Is At Risk for Rh Incompatibility?")

Unless you were treated with Rh immune globulin after each of these events, you're at risk for Rh incompatibility during current and future pregnancies.

It's important to let your doctor know about your risk early in your pregnancy. Once your doctor is aware of your risk, he or she can carefully monitor your pregnancy and promptly treat any problems that arise.

Key Points

• Rh incompatibility is a condition that occurs during pregnancy if a woman has Rh-negative blood and her baby has Rh-positive blood.
• "Rh-negative" and "Rh-positive" refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells. If you have Rh factor, you’re Rh-positive. If you don’t have it, you’re Rh-negative. Rh factor is inherited (passed from parents to children through the genes). Most people are Rh-positive.
• When you’re pregnant—especially during delivery—blood from your baby can cross into your bloodstream. If you’re Rh-negative and your baby is Rh-positive, your body will create antibodies (proteins) against the baby’s Rh-positive blood.
• These antibodies usually don’t cause problems during a first pregnancy. This is because the baby often is born before many of the antibodies develop. However, the antibodies stay in your body once they have formed. Thus, Rh incompatibility is more likely to cause problems in second or later pregnancies (if the baby is Rh-positive).
• The Rh antibodies can cross the placenta and attack the baby’s red blood cells. This can lead to hemolytic anemia in the baby.
• Hemolytic anemia is a condition in which red blood cells are destroyed faster than the body can replace them. Without enough red blood cells, the body won’t get enough oxygen. This can lead to serious problems or death in newborns.
• An Rh-negative woman who conceives a child with an Rh-positive man is at risk for Rh incompatibility. If you’re Rh-negative and the father of your baby is Rh-positive, there’s a 50 percent or more chance that the baby will have Rh-positive blood.
• If you’re Rh-negative, your risk for Rh incompatibility also increases if you were exposed to Rh-positive blood before your current pregnancy. This could have happened during an earlier pregnancy, a miscarriage, an induced abortion, a blood transfusion, or certain tests (such as amniocentesis and chorionic villus sampling).
• Rh incompatibility is diagnosed with blood tests. To determine whether a baby is developing hemolytic anemia and how serious it is, doctors may use more advanced tests, such as ultrasound.
• Rh incompatibility is treated with a medicine called Rh immune globulin. If you’re diagnosed with the condition during pregnancy, you’ll receive Rh immune globulin in your seventh month of pregnancy and again within 72 hours of delivery.
• Treatment for a baby who has hemolytic anemia will vary depending on how severe the condition is.
• Rh incompatibility can be prevented with Rh immune globulin, as long as the medicine is given at the correct times. Once you have formed Rh antibodies, the medicine will no longer help.
• With prompt and proper prenatal care and screening, you can prevent the problems of Rh incompatibility. Once your doctor is aware of your risk, he or she can carefully monitor your pregnancy and promptly treat any problems that arise.

Links to Other Information About Rh Incompatibility

NHLBI Resources

• Hemolytic Anemia (Diseases and Conditions Index)

Non-NHLBI Resources

• Rh Incompatibility (MedlinePlus)

Clinical Trials

• Current Research (ClinicalTrials.gov)