The Rh Factor: How It Can Affect Your Pregnancy

What is the Rh factor?

The Rh factor is a type of protein found on red blood cells. A simple blood test can be used to determine if you are Rh positive (having the Rf factor) or Rh negative (not having the Rh factor). Most people are Rh positive, but being Rh negative does not affect a person’s general health. Issues may arise in pregnant women if the mother is Rh negative and the fetus is Rh positive. In most cases, problems due to the Rh factor can be prevented with special medication.

When does the Rh factor cause problems?

The Rh factor causes problems when the blood of the Rh positive fetus and the blood of the Rh negative mother come into contact. This causes the women with Rh negative blood to become sensitized, producing antibodies that fight the Rh factor as if it were a harmful substance.

Sensitization only occurs when an Rh negative women is pregnant with an Rh positive fetus. When a mother is Rh negative, the fetus can only be Rh positive if the father is Rh positive. If both parents are Rh negative, there is no chance the fetus will be Rh positive and the mother has no risk of becoming sensitized. If the women is Rh positive and the father is Rh negative, the sensitization does not occur.

During pregnancy, the mother and fetus do not share blood systems, but a small amount of fetus blood can travel across the placenta into the mother’s system. When this occurs, a small number of women with Rh negative blood will react as if allergic to the fetus and produce antibodies. These antibodies will attack the blood of the Rh negative fetus and break down fetal red blood cells. This causes anemia, which can lead to serious illness, brain damaged, or even death of the fetus.

Once formed, antibodies do not disappear from the mother’s system. The first pregnancy with an Rh positive fetus may not give enough time for the women’s body to develop many antibodies, so serious problems might not occur. A second pregnancy with an Rh positive fetus is more likely to experience anemia in the fetus and become worse in later pregnancies.

Sensitization can occur in a women any time her blood is mixed with Rh positive blood. This can develop if the Rh negative women has once had:

  • 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 can determine a women’s blood type and Rh factor. Another test called an antibody screen, can show if an Rh negative woman has developed antibodies to Rh positive blood.

Rh immunoglobulin (RhIg) is a blood product that can prevent an Rh negative mother from responding to Rh positive blood cells of a fetus and becoming sensitized. Sensitization is preventable in almost all cases by RhIg, but is not helpful if a mother is already sensitized.

RhIg is injected in the muscle of the arm or buttocks with common side effects of soreness near the injected area or a slight fever. Side effects usually disappear on their own.

When is treatment needed?

During Pregnancy and After Delivery
A woman with Rh negative blood who has not been sensitized may be treated with RhIg around the 28th week of pregnancy to prevent sensitization for the duration of the pregnancy. Women who have passed their due date may receive another dose of RhIg as determined by their doctor.

A Rh negative mother who gives birth to a child with Rh positive blood should be given another dose of RhIg shortly after birth. This dose is suggested to prevent the production of antibodies by the mother brought on by Rh positive blood cells received from the baby during and after birth. Treatment is not necessary for babies born with Rh negative blood.

RhIg treatment is only effective for one pregnancy and should be repeated for each future pregnancy and delivery.

A woman may receive RhIg treatments after birth, despite sterilization for the following reasons:

  1. The woman may decide to have the sterilization reversed.
  2. There is a slight chance the sterilization may fail to prevent another pregnancy.
  3. Preventing the development of antibodies can be beneficial if blood transfusions are needed in the future. Antibodies make matching blood types harder for transfusions.

Other Reasons for RhIg Treatment
Rh negative women should seek treatment if their blood comes in contact with their fetus. This may occur during a miscarriage, ectopic pregnancy or induced abortion. RhIg may also be given after certain procedures, such as amniocentesis or chorionic villus sampling to prevent the formation of antibodies that would attack future Rh positive fetuses.

What happens if antibodies develop?

RhIg treatment is not effective against antibodies developed by an Rh negative woman. A mother who is Rh sensitized will be checked during her pregnancy to see if the fetus is at risk.

In severe cases, a fetus with anemia may be delivered early or given blood transfusions while still in the mother’s uterus. Less severe cases allow the baby to be delivered at a normal time, but may require a transfusion for the baby to replace blood cells.