Rh Factor
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Rh Factor

What is Rh Factor?

Rh factor is a type of protein in the red blood cells. The majority of people have Rh factor and are called Rh positive. Those who do not have the Rh factor are called Rh negative. A simple and quick blood test can determine whether you are Rh positive or Rh negative. Although the presence or absence of Rh factor does not affect your health, it can cause problems during pregnancy.

An Rh negative mother and an Rh positive father can conceive an Rh positive child. Although the mother and fetus have separate blood systems, blood from the Rh positive fetus can cross the placenta into the mother's body. In a small number of Rh negative women, problems can arise because their bodies encounter the Rh factor in the fetal blood as if it were a harmful substance. These women then produce antibodies to fight the fetal Rh positive red blood cells. This breaks down the red blood cells of the fetus and causes anemia known as hemolytic disease. If severe enough, hemolytic disease can cause brain damage or even death in the fetus or newborn.

Once produced, the Rh factor antibodies do not disappear from the woman's body. Though they may not effect a first pregnancy, they are more likely to cause hemolytic disease in the fetus in subsequent pregnancies. There are other cases where fetal blood that might be Rh positive can mix with maternal Rh negative blood, resulting in the development of Rh factor antibodies. Such cases include miscarriage, induced abortion, ectopic (tubal) pregnancy, and very seldom, women who have amniocentesis later in pregnancy.

How can hemolytic disease be prevented?

Hemolytic disease can be prevented as long as the Rh negative woman has not made Rh factor antibodies from an earlier pregnancy or blood transfusion. A simple blood test can determine whether a woman has Rh negative or Rh positive blood. Another blood test called an antibody screen can detect if an Rh negative woman has developed antibodies to Rh positive blood.

An Rh negative woman who has not yet developed antibodies to Rh positive blood can be given Rh immunoglobulin (Rhogam). Rhogam suppresses her ability to respond to Rh positive red blood cells. Rhogam is injected into the muscle of the arm or buttocks. It is safe for pregnant women. Side effects are temporary and may include soreness from the injection or slight fever.

Protection from Rhogam lasts only about 12 weeks. A repeat dosage of Rhogam is needed for each pregnancy and delivery of an Rh positive child. It is recommended that Rh negative women receive treatment with Rhogam after an ectopic pregnancy, miscarriage, or induced abortion. This will reduce the risk of developing antibodies that could cause problems in a future pregnancy with an Rh positive fetus. An Rh negative woman who has amniocentesis may be treated with Rhogam as well. She has a slight risk of developing antibodies because the procedure could cause a mixing of the fetal Rh positive blood cells with the mother's Rh negative blood.

If antibodies have already developed...

If antibodies have already developed, it does not help to treat a woman with Rhogam. Instead, health care providers must take measures to protect the fetus. Such measures may include:

  • Checking to see if the fetus has developed hemolytic disease
  • Determining the appropriate time for delivery
  • A blood transfusion after delivery that will replace the diseased blood cells with healthy blood

In severe cases, measures may include:

  • Early delivery of the baby
  • Blood transfusion to the fetus

Recommendations for reducing the incidence of hemolytic disease

  • All pregnant women should have a blood test early in the pregnancy.
  • If the mother's blood is found to be Rh negative, the father's blood should be tested to determine the risk of having an Rh positive baby.
  • Rhogam should be given to women who are at risk for having a child with hemolytic disease.
  • Every pregnant woman should have regular health care.

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