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Fetal-maternal erythrocyte distribution

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Fetal-maternal erythrocyte distribution

Definition:

The fetal-maternal erythrocyte distribution test is used to measure the number of fetal red blood cells in a pregnant woman's blood. (See also Rh incompatibility.)

Alternative Names:
Kleihauer-Betke stain

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How the test is performed:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

The sample is taken to the laboratory where the hemoglobin is removed and both fetal and maternal red blood cells are counted. Based on that count a ratio of fetal to maternal blood cells is determined.

How to prepare for the test:

No special preparation is necessary for this test.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

Rh incompatibility occurs when the mother's blood type is Rh-negative and her unborn baby's blood type is Rh-positive. If the mother is Rh-positive, or if both parents are Rh-negative, there is no reason to worry about Rh incompatibility.

However, if the mother is Rh-negative and the baby's father is Rh-positive, then most likely the baby will inherit the father's blood type, creating incompatibility between mother and fetus. In this case, if some of the baby's blood gets into the mother's blood stream, her body will produce antibodies. These antibodies could pass back through the placenta and harm the developing baby's red blood cells, causing very mild to very serious anemia in the fetus.