RH Factor

What is the Rh Factor?

The Rh factor is a type of protein found on red blood cells. Most individuals have the Rh factor and are considered Rh-positive, while others do not have it and are considered Rh-negative. A simple blood test during pregnancy can determine whether you are Rh-positive or Rh-negative.

While the Rh factor doesn’t affect overall health, it can cause issues during pregnancy. However, these problems can usually be prevented by taking special medications. Therefore, all women in the early stages of pregnancy should undergo a blood test to guard against Rh sensitization.

When does the Rh Factor cause problems?

The Rh factor causes problems when Rh-negative blood comes into contact with RH-positive blood. If this occurs, the RH-negative individual may become sensitized, producing antibodies that perceive the Rh factor as a harmful substance.

During pregnancy, the woman and fetus do not share blood systems. However, a small amount of fetal blood can cross the placenta into the woman’s system. In some cases, Rh-negative women carrying Rh-positive fetuses may react as if they are allergic to the fetus. This leads to sensitization, where the mother produces antibodies that attack the fetal red blood cells, causing anemia. Severe cases can result in serious illness, brain damage, or even death of the fetus or newborn.

Once these antibodies form, they do not disappear. During a first pregnancy with a Rh-positive fetus, the baby is often born before the antibodies develop, potentially avoiding serious problems. However, in subsequent pregnancies with Rh-positive fetuses, these antibodies are more likely to cause fetal anemia. This condition tends to worsen in later pregnancies.

A woman can become sensitized whenever Rh-positive blood mixes with her own blood. This can happen if an Rh-negative woman has:

• A miscarriage
• An induced abortion
• An ectopic pregnancy
• A blood transfusion
• Amniocentesis
• Chorionic villus sampling (CVS)
• Bleeding during pregnancy

How can problems be prevented?

A simple blood test during pregnancy will identify Rh factor. An additional blood test called an antibody screen, can show if a Rh-negative woman has developed antibodies to Rh-positive blood.

Anemia can be prevented in the fetus if the woman has not yet made antibodies against the Rh factor. Rh immunoglobulin (RhIg) is a blood product that can prevent a Rh-negative mother from being sensitized, by preventing her body from responding to Rh-positive blood cells of the fetus.

If a Rh-negative woman is given RhIg it will likely be injected into a muscle of the arm or buttocks. Side effects include soreness at the injection site or a slight fever. Usually both will go away on their own.

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. This will prevent problems in a small number of women who can become sensitized during the last three months.

After birth, if the child has Rh-positive blood, the mother will be given another dose of RhIg. This prevents the woman from producing antibodies against Rh-positive blood cells she may have been exposed to during delivery. If the baby is Rh-negative, no treatment is needed.

For future pregnancies and deliveries, the mother will require a repeat dose of RhIg for each Rh-positive child.

What happens if antibodies develop?

If a woman has already developed antibodies, RhIg treatment will not help. A mother who is Rh-sensitized will be checked during her pregnancy to see if the fetus is at risk. In some severe cases, a baby with anemia may be given blood transfusions while in the uterus or delivered early. In less severe cases, the baby may need a transfusion after delivery to replace the blood cells.