What is the Rh Factor?

Just as there are different major blood groups, such as A and B type blood, there also is an Rh factor.  The Rh factor is the type of protein on the red blood cells.  Most people have the Rh factor --- they are Rh positive.  Others do not have the Rh factor --- they are Rh negative.  A simple lab test can tell whether you are Rh positive or Rh negative. 

The Rh factor does not affect a person's general health.  It can cause problems during pregnancy, though.  These problems can be prevented in most cases with the use of a special drug. 

When Does the Rh Factor Cause Problems?

The Rh factor causes problems when an Rh-negative person's blood comes in contact with an Rh-positive blood.  If this contact occurs, the person with Rh-negative blood may become sensitized.  This means he or she produces antibodies to fight the Rh factor as if it were a harmful substance.

An Rh-negative woman can become sensitized if she is pregnant with an Rh-positive fetus.  If a pregnant woman's blood group is Rh negative, knowing whether the father is Rh positive or Rh negative will help find the risk of Rh sensitization.  An Rh-negative mother and an Rh-positive father can conceive and Rh positive child

During pregnancy, mother and fetus do not share blood systems.  Blood from the fetus can cross the placenta into the mother's system, though.  When this occurs, a small number of pregnant women with Rh-negative blood who carry an Rh-positive fetus will react as if it were allergic to the fetal blood.  Then, they become sensitized by making antibodies.  These antibodies go back to the fetus and attack the fetal blood.  They break down the red blood cells and produce anemia (lack of iron in the blood).  This condition is called hemolytic disease.  It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn.   

Once formed, these antibodies do not go away.  In a first pregnancy with an Rh-positive fetus, the baby often is born before the mother's body develops many antibodies.  A small number of these pregnancies start having problems during the last 3 months.

Sensitization can occur any time the fetus' blood mixes with the mother's blood.  It can occur if an Rh-negative woman has once had:

• A miscarriage
• An induced abortion
• An ectopic pregnancy

A woman also can become sensitized if she has ever had a blood transfusion.

How Can Problems Be Prevented?

A simple blood test can tell a woman's blood type and Rh factor.  Another blood test. called and antibody screen, can show if an Rh-negative woman has developed antibodies to Rh-positive blood.

Hemolytic disease can be prevented if the Rh-negative woman has not made antibodies against the Rh factor.  Rh immunoglobulin (RhIg) is a blood product that can prevent sensitization of an Rh-negative mother.  It keeps her body from being able to respond to Rh-positive cells.

RhIg, first used in 1968, is safe and easily obtained.  Its use can prevent sensitization in almost all cases.  RhIg is not helpful if the mother is already sensitized, though.

If an Rh-negative woman is given  RhIg, it likely will be injected into a muscle of the arm or buttocks.  RhIg is safe for a pregnant woman to use.  The only know side effects are a soreness where the drug was injected or a slight fever.  Both side effects will go away.

When is RhIg Used?

During Pregnancy and After Delivery

If a woman with Rh-negative blood has not been sensitized, her doctor may suggest that she receive RhIg around the 28th week of pregnancy to prevent sensitization for the rest of the pregnancy.  This takes care of the small number of women who can become sensitized during the last 3 months of pregnancy.

Shortly after birth, if the child has Rh-positive blood, the mother should be given another dose of RhIg.  In almost all cases, this treatment prevents the woman from making antibodies to the Rh-positive cells she may have received from her fetus before and during delivery.  No treatment is needed if the father or baby is also Rh negative. 

The treatment is good only for the pregnancy in which it is given.  Each pregancy and delivery of an Rh-positive child requires repeat doses of RhIg. 

Rh-negative women also should receive treatment after any miscarriage, ectopic pregnancy, or induced abortion.  This prevents any chance of the woman developing antibodies that would attack a future Rh-positive fetus.

Other Reasons RhIg May Be Given

Amniocentesis.  Amniocentesis is a procedure in which a small amount of amniotic fluid (the fluid in the sac that surrounds the fetus) is withdrawn from the mother's uterus through a needle for testing.  This can help detect certain birth defects in the fetus during pregnancy.  If and when this is done, fetal Rh-positive red blood cells could mix with a mother's Rh-negative blood.  This would cause her to produce antibodies.  Thus, RhIg is given. 

Postpartum Sterilization.  An Rh-negative mother may receive RhIg after a birth even if she decides to have her fallopian tubes tied and cut to prevent future pregnancies.  Treatment might be given for three reasons:

1. The woman may decide later to try to have the sterilization reversed.
2. There is a slight chance that the sterilization mat fail to prevent pregnancy. 
3.  The treatment prevents her from developing antibodies in case she ever needs to be given a blood transfusion in the future.  The presence of antibodies makes matching blood types for transfusions harder.

RhIg is not always given in this instance.  A woman should talk to her doctor about it.

What Happens if Antibodies Develop?

Once a woman develops antibodies, RhIg  treatment does not help.  Doctors are finding ways to save infants who get hemolytic disease.  A mother who is Rh-sensitized will be checked during her pregnancy to see if the fetus is developing the disease.

In some cases of hemolytic disease, the doctor may suggest delivery at the normal time.  Delivery may be followed by a type of transfusion for the baby that will replace the diseased blood.  For more severe cases, the baby may be delivered early or given transfusion while still in the mother's uterus.

Finally.....

To protect against Rh sensitization, all pregnant women should have a blood test done at an early stage of pregnancy. RhIg, given when needed, protects women who may develop Rh antibodies.

GLOSSARY

Antibodies: Proteins in the blood produced in reaction to foreign substances, such as bacteria that causes infections.

Ectopic Pregnancy: A pregnancy in which the fertilized egg begins to grow in a place other than inside the uterus, usually in the fallopian tubes.

Induced Abortion: The planned termination of a pregnancy before the fetus can survive outside the uterus.

Placenta: Tissue that connects mother and fetus and provides nourishment to and take away waste from the fetus.

Rh Immunoglobulin (RhIg): A substance given to prevent an Rh-negative person's antibody response to Rh-positive blood cells.

Transfusion: Direct injection of whole blood or plasma into the blood stream.