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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 who have hemolytic anemia and related problems. A pediatrician is a doctor who specializes in treating children. A hematologist is a doctor who specializes in treating people who have 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 too, the baby has no chance of having Rh-positive blood. Thus, there's no risk of Rh incompatibility.

However, if the baby's father is Rh-positive, the baby has a 50 percent or more chance of having 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 it's not possible to find out his Rh status, 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. (Rarely, an amniocentesis can expose you to Rh-positive blood).

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 chance that the baby has 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 a test called 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 risk of hemolytic anemia. This is because the anemia will cause the baby's heart to pump more blood.

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January 01, 2011 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.

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