Prenatal Testing Basics: Rh Factor Test

What it is, who has it, when, why, and what it tells you.

When is the test taken?

You'll be tested for Rh factor early in pregnancy -- often when your blood sample is taken during your first prenatal care visit.

Who needs to take the test, and why?

The Rh factor test is routine for nearly all pregnant women. The test is needed to ensure that the Rh factor, a protein on the surface of red blood cells, is present in your blood. This information is important because, in cases when the mother does not carry the Rh factor and the baby does (having inherited it from the father), the mother's body may react by producing antibodies that attack the baby's blood cells. These antibodies can cause complications ranging from newborn jaundice to stillbirth. However, early detection of Rh factor problems can dramatically reduce such dangers.

What's involved?

Blood is taken through a small needle, usually from a vein in the arm. The sample is then sent to a lab for analysis.

When are test results available, and how are they interpreted?

Test results are available within a few days. If your blood sample reveals that the Rh factor is not present, you are considered "Rh-negative." Your blood will be taken again at 28 weeks to be tested for antibodies. If you don't have antibodies, you'll be given an injection of Rh-immunoglobulin (RhIg), which prevents your body from producing them and thus protects the baby from harm. If you do have Rh antibodies, you will be monitored closely. If antibody levels become too high, special measures, including blood transfusions to the baby and early delivery, may be taken.

All content here, including advice from doctors and other health professionals, should be considered as opinion only. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.

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