Definition of Fetal-maternal erythrocyte distribution:

The fetal-maternal erythrocyte distribution test is used to measure the number of the unborn baby's red blood cells in a pregnant woman's blood.

See also: Rh incompatibility

How the test is performed:

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. 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 the baby's and mother's red blood cells are counted.

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

If the baby's blood is Rh+ and gets into the mother's Rh- bloodstream, her body will produce antibodies. These antibodies could pass back through the placenta and harm the developing baby's red blood cells. This can cause mild to serious anemia in the unborn baby.

This test determines the amount of blood that has been exchanged between the mother and fetus. All Rh- pregnant women should get this test if they have bleeding or a risk of bleeding during the pregnancy.

In a woman whose blood is Rh incompatible with her infant, this test helps determine how much Rh immune globulin (RhoGAM) she must receive to prevent her body from producing abnormal proteins that attack the unborn baby in future pregnancies.