Rh Factor

Just as there are different major blood groups, such as type A and type B, there also is an Rh factor. The Rh factor is a protein that can be present on the surface of red blood cells. Most people have the Rh factor—they are Rh positive. Others do not have the Rh factor—they are Rh negative.

The Rh factor is inherited—passed down through parents’ genes to their children.

The Rh factor can cause problems if you are Rh negative and your fetus is Rh positive. This is called Rh incompatibility. These problems usually do not occur in a first pregnancy, but they can occur in a later pregnancy.

When an Rh-negative patient’s blood comes into contact with blood from their Rh-positive fetus, it causes the Rh-negative patient to make antibodies against the Rh factor. These antibodies attack the Rh factor as if it were a harmful substance. A person with Rh-negative blood who makes Rh antibodies is called "Rh sensitized."

During pregnancy, the patient and fetus do not share blood systems. However, a small amount of blood from the fetus can cross the placenta into the patient’s system. This sometimes may happen during pregnancy, labor, and birth. It also can occur if an Rh-negative patient has had any of the following during pregnancy:

• D&C or abortion
• Miscarriage or Ectopic pregnancy
• Amniocentesis / Chorionic villus sampling (CVS)
• Bleeding during pregnancy
• Blunt trauma to the abdomen during pregnancy

During an Rh-negative patient’s first pregnancy with an Rh-positive fetus, serious problems usually do not occur because the baby often is born before the patient’s body develops many antibodies. If preventive treatment is not given during the first pregnancy and the patient later becomes pregnant with an Rh-positive fetus, the baby is at risk of Rh disease.

Problems during pregnancy can occur when Rh antibodies from an Rh-sensitized patient cross the placenta and attack the blood of an Rh-positive fetus. The Rh antibodies destroy some of the fetal red blood cells. This causes hemolytic anemia, where red blood cells are destroyed faster than the body can replace them.

Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, the fetus will not get enough oxygen. Hemolytic anemia can lead to serious illness. Severe hemolytic anemia may even be fatal to the fetus.

Yes. If you are Rh negative, you can be given a shot of Rh immunoglobulin (RhIg) (i.e. RhoGAM). RhIg is made from donated blood. When given to a non-sensitized Rh-negative person, it targets any Rh-positive cells in the bloodstream and prevents the production of Rh antibodies. When given to an Rh-negative patient who has not yet made antibodies against the Rh factor, RhIg can prevent fetal hemolytic anemia in a later pregnancy.

• General precautions: prior history of severe systemic allergic reactions to human immune globulin; IgA deficient individuals
• Side Effects:
  • Common: local reactions including swelling, induration, redness, and mild pain at the site of injection; possible slight elevation in temperature
  • Rare: systemic reactions such as allergic reactions including hives, generalized urticaria, tightness of chest, wheezing, hypotension (low blood pressure) and anaphylaxis; transmission of infectious agents (RhIg is a blood product that could theoretically transmit blood-borne infections)