Just as there are different major blood groups, such as A and B type blood, there is also an Rh factor--a type of protein on the red blood cells.  Most people have the Rh factor and are said to be Rh positive.  Others do not have the Rh factor and are thus Rh negative.  Today, a simple lab test quickly determines 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, however.  Now, with the use of a special drug, these problems can almost always be prevented. 

When Does the RH Factor Cause Problems for a Pregnancy?
How Is Hemolytic Disease Prevented?
When Is Rhogam Used?
Other Reasons Rhogam May Be Given
What Happens If Antibodies Develop?

When Does the Rh Factor Cause Problems for a Pregnancy? 

The Rh factor causes problems when an Rh-negative person's blood (without Rh factors) comes in contact with Rh-positive blood (with Rh factor).  The person with Rh-negative blood may then become sensitized.  This means he or she produces antibodies to fight the Rh factor as if it were a harmful substance.  Sensitization can occur if an Rh-negative woman becomes pregnant with an Rh-positive fetus.  An Rh-negative mother and an Rh-positive father can conceive an Rh-positive child.  The Rh-negative woman's body may produce antibodies that then attack the fetal Rh-positive red blood cells. 

During pregnancy, although mother and fetus have separate blood systems, blood from the fetus can cross the placenta (an organ connecting mother and fetus that brings nourishment and takes away waste) into the mother's system. A small number of pregnant women with Rh-negative blood who carry an Rh-positive fetus will react to the fetal blood as a foreign substance and become sensitized by making antibodies.  These antibodies then go back to the fetus and attack the fetal blood, breaking down the red blood cells and producing anemia.  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 disappear.  In a first pregnancy with an Rh-positive fetus, the baby is usually delivered before the mother's body develops significant amounts of antibodies, although a small percentage of these pregnancies develop problems during the last 3 months.  In a second pregnancy with an Rh-positive fetus, the antibodies are more likely to cause hemolytic disease in the fetus. The condition usually becomes worse in later pregnancies. 

Sensitization can also occur if an Rh-negative woman has had a previous miscarriage, induced abortion, or ectopic pregnancy (pregnancy in the tubes).  There is also a slight chance that a woman may develop antibodies after having amniocentesis done later in pregnancy.  These are all cases in which fetal blood (that might be Rh positive) could mix with maternal blood, resulting in the production of antibodies that could complicate a subsequent pregnancy. 

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How Is Hemolytic Disease Prevented? 

Today, hemolytic disease can for the most part be prevented if the Rh-negative woman has not already made antibodies against the Rh factor from an earlier pregnancy or blood transfusion.  Rh immunoglobulin (Rhogam) is a product that can safely prevent sensitization of an Rh-negative mother.  It suppresses her ability to respond to Rh-positive red cells. With its use, sensitization can be prevented almost all the time, although Rhogam is not helpful if the mother is already sensitized. 

A simple blood test can tell a woman what her blood type and Rh factor are.  Another blood test, called an antibody screen, can show if an Rh-negative woman has developed antibodies to Rh-positive blood. 
If an Rh-negative woman is given Rhogam, it is injected into a muscle of the arm or buttocks.  She will be "passively immunized."  This means that her body will not make antibodies that might otherwise attack the red blood cells of her Rh-positive fetus. 

Rhogam is safe for a pregnant woman to use.  The only known side effects are a soreness where the drug was injected or a slight fever.  Both are temporary reactions. 

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When Is Rhogam Used?

During Pregnancy and After Delivery  
If a woman with Rh-negative blood has not been sensitized (has not developed Rh antibodies), her health care provider may recommend that she receive Rhogam 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.  Shortly after birth, if the child has Rh-positive blood, the mother should be given another dose.  This treatment nearly eliminates all chances of developing 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.  Protection seems to last only about 12 weeks.  Each pregnancy and delivery of an Rh-positive child requires repeat doses of Rhogam.  Rh-negative women should also 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. 

Rhogam may also be given if an Rh-negative woman has amniocentesis. Amniocentesis is a procedure in which a small amount of amniotic fluid (the fluid in the sac surrounding 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, causing her to produce antibodies; thus, Rhogam is given. 

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What Happens if Antibodies Develop?

Once a woman develops antibodies, Rhogam treatment does not help.  However, health care providers are finding ways to save infants who get hemolytic disease.  An Rh-sensitized mother will be checked during her pregnancy to see if the fetus is developing the disease.  In some cases of hemolytic disease, the health care provider may recommend delivery at the normal time.  Delivery may be followed by a type of transfusion for the baby that will replace the diseased blood cells with healthy blood.  For more severe cases, the baby may be delivered early or given transfusions while still in the mother's womb. 
 

Finally . . . 

 Today, of all Rh-negative women who run the risk of developing Rh sensitization, most have received treatment to prevent them from developing antibodies to Rh-positive blood.  Hospitals are working with health care providers and their patients to try and reach the remaining women to prevent the 5,000 cases of hemolytic disease that still occur each year.  Safeguards can be taken against Rh sensitization: 

• All pregnant women should have a blood test done at an early stage of pregnancy. 
• If a pregnant woman's blood group is Rh negative, knowing whether the father is Rh positive or Rh negative will help identify the risk of Rh sensitization. 
• Rhogam, given when needed, provides protection for women who have a chance of developing Rh antibodies. 
• For every woman, a routine of regular health care before her baby is born is the first step in ending the problem. 

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