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If you are pregnant, you will have your first prenatal tests during your first trimester. At your first prenatal visit, every woman has her blood tested to see what her blood type is. If your blood is Rh-negative, it will also be tested for antibodies to Rh-positive blood. If you have antibodies, that means that you have been sensitized to Rh-positive blood. The antibodies can now kill Rh-positive red blood cells.

If you are Rh-negative and your partner is Rh-positive, your fetus is likely to be Rh-positive.

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If you are pregnant or have miscarried, or if you have had an elective abortion, a partial molar pregnancy, or an ectopic pregnancy, you will need testing to see if you have been sensitized to Rh-positive blood.

If you are Rh-negative

All pregnant women have an indirect Coombs' test during early pregnancy.

At the first prenatal visit, your blood is tested to see if you have been previously sensitized to Rh-positive blood. If you are Rh-negative and test results show that you are not sensitized, a repeat test may be done between 24 and 28 weeks.
If test results at 28 weeks show that you have not been sensitized, no additional tests for Rh-related problems are done until delivery (barring complications such as placenta abruptio). You will also have a shot of Rh immune globulin. This lowers your chances of being sensitized during the last weeks of your pregnancy.
If your newborn is found to be Rh-positive, your blood will be screened again at delivery with an indirect Coombs' test to see if you have been sensitized during late pregnancy or childbirth. If you have not been sensitized, you will have another shot of Rh immune globulin.

If you are sensitized to the Rh factor

If you are already Rh-sensitized or become sensitized while pregnant, close monitoring is important to determine whether your fetus is being harmed.

If possible, the father will be tested to see if the fetus could be Rh-positive. If the father is Rh-negative, the fetus is Rh-negative and is not in danger. If the father is Rh-positive, amniocentesis will probably be used to learn the fetus's blood type. In some medical centers, the mother's blood can be tested to learn her fetus's blood type. This is a new test that is not widely available.
An indirect Coombs' test is done periodically during your pregnancy to see if your Rh-positive antibody levels are increasing. This is the typical course of treatment for most sensitized women during pregnancy.
Fetal Doppler ultrasound of blood flow in the brain shows fetal anemia and how bad it is. At a medical center with Doppler experts, this test can give you the same anemia information as amniocentesis, without the risks.³
Amniocentesis may be done:
- At or after 15 weeks to check amniotic fluid for signs of fetal problems.
- To learn the fetal blood type and Rh factor.
- On a repeated basis to check fetal anemia. This tells how much a fetus is being affected by sensitization.
Fetal blood sampling (cordocentesis) may be done to directly assess your fetus's health. This procedure is used on a limited basis, usually for monitoring known sensitization problems (as when a mother has had previous fetal deaths, or when other testing has shown signs of fetal distress).
Electronic fetal heart monitoring (nonstress test) may be done in the third trimester to check your fetus's condition. Unusual fetal heart rhythms detected during a nonstress test may be a sign that the fetus has anemia related to the sensitization.
Fetal ultrasound testing can be used as a pregnancy progresses to detect sensitization problems, such as fetal fluid retention (a sign of severe Rh disease).

Early Detection

Early prenatal Rh blood typing and testing for Rh sensitization is necessary to ensure that every vulnerable fetus can be properly monitored and treated.

WebMD Medical Reference from Healthwise

Last Updated: October 22, 2009

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.