Rh Factor

August 16, 2010



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What is Rh Factor?

Rh factor, or Rhesus factor, is a type of protein which is present in the red blood cells of most people. If the Rh factor is present in a person’s blood, they are considered to be Rh positive. If a person does not have Rh factor in their blood, they are considered to be Rh negative.

The presence or lack of Rh is not good or bad and has no bearing on a person’s health.

What is Rh Incompatibility?

Whether a person is Rh positive, or Rh negative is only important in two situations, when a person is receiving a blood transfusion, and during pregnancy.

When two blood types are mixed together, this can cause what is known as Rh incompatibility. In Rh incompatibility, Rh factor acts like a powerful antigen and can induce an intense reaction.

When an Rh negative person’s blood comes in contact with and Rh positive person’s blood, the Rh factor is greeted as an antigen. The Rh negative blood begins to produce antibodies to attack the antigen, which it views as a harmful intruder.

These antibodies are called anti-Rh agglutinins. They connect themselves to Rh positive blood cells and cause them to agglutinate, or clump together. This generally results in the destruction of red blood cells, which is called hemolysis. If this clumping and destruction of blood cells gets too intense, a serious and possibly life threatening condition can develop.

During pregnancy, Rh incompatibility occurs when the pregnant mother and her fetus have a different Rh blood type. If blood from the fetus enters the mother’s blood stream, it can result in the formation of agglutinins. The mother’s body acts, in essence as if the fetus is an allergen to which she is allergic.

If left unmonitored, Rh incompatibility can lead to fetal anemia, a condition which causes red blood cells to be destroyed in the baby. This could result in brain damage or death to the fetus.

Rh incompatibility is generally most problematic, and more likely to result in fetal anemia in a second pregnancy or later. This is because once antibodies develop, they stay in the mother’s blood forever. Each pregnancy may cause a subsequently greater concentration of antibodies in the mother’s blood stream.

The presence of Rh antibodies is also known as Rh sensitization.

How Is Rh Incompatibility Diagnosed?

Rh incompatibility is diagnosed through a simple blood test, which determines your blood type and identifies your Rh factor. If the mother is Rh positive, then there is no issue of incompatibility. Approximately 85 percent of the population is Rh positive.

If the mother is Rh negative, the baby’s father will be tested to determine if he is Rh positive or negative. If the father’s blood is also Rh negative, there is no issue of incompatibility. If the baby’s father is Rh positive, there is a possibility that the baby may be Rh positive also, which could cause an incompatibility.

How is Rh Incompatibility Treated?

If the mother is Rh negative, a blood test called an antibody screen will be performed. This test tells whether or not the Rh negative mother has developed antibodies to Rh factor.

If the Rh negative mother has not produced any antibodies, she may be given a vaccine-like injection of a substance called Rh immune globulin, which is known as Rhogam. Rhogam will help prevent Rh sensitization, or antibodies from developing.

Rh immune globulin (RhIg) injections can help prevent Rh sensitization in most women, but is not effective in a case where sensitization has already occurred.

RhIg is usually administered at 28 weeks of gestation, and again if a pregnancy goes past the due date. After birth the Rh negative mother will be given another injection of RhIg in order to prevent Rh antibodies from developing in the event of future pregnancies or blood transfusions.

If a woman has already developed Rh antibodies and is Rh sensitized, she will be closely monitored throughout her pregnancy to determine if her baby is at any risk.

If the fetus has been found to have anemia, it may be given blood transfusions while still in the womb or delivered early. In some cases, it may be possible to carry the baby full term without intervention. If necessary, the baby will be given a blood transfusion following delivery.

It is important for all pregnant women to have a blood test in early pregnancy to discover their Rh factor. If detected early, the best treatment is RhIg injections that help prevent antibodies from developing.




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