Rh Factor and Isoimmunization

What is Rh Factor?

The Rh factor is a special protein that coats the red blood cells in your body. Most people make the protein, and have Rh positive blood type. A smaller number of people do not make this protein and are known as having Rh negative blood type.

What is Rh Sensitization?

If a person with Rh negative blood gets exposed to Rh positive blood, she can make antibodies to the Rh proteins. This is called "sensitization". Events that cause exposure to Rh positive blood include pregnancy, miscarriage, trauma or bleeding during pregnancy, childbirth or blood transfusions.

If an Rh negative woman becomes sensitized and is pregnant with an Rh positive baby, the antibodies are able to cross the placenta and may cause anemia in the baby.

What if I am Rh Negative?

If you are Rh negative, it is recommended you receive an injection of RhoGam during pregnancy and, if your baby is found to have the Rh positive blood type, postpartum. RhoGam is a product derived from human plasma that can prevent antibodies to the Rh protein from forming.

Before RhoGam was routinely administered, the incidence of sensitization for women with Rh negative blood was around 15%. With a single dose of RhoGam during pregnancy (around 7 months), the incidence of sensitization is less than 5%. If your baby is Rh positive, a dose of RhoGam during pregnancy and within 72 hours after delivery will reduce the rate of sensitization to less than 1%.