Your blood is checked for a substance called the Rh factor as part of your physical examination. If your blood contains this factor, you are Rh positive. If your blood does not contain it, you are Rh negative.
There are no problems if:
- The mother has the Rh factor (Rh positive)
- Neither parent has the Rh factor (both are Rh negative)
However, if you are Rh negative and the father is Rh positive, there is a possibility that the baby’s blood may also be Rh positive (the opposite of yours). In this case, your body may manufacture a substance called Rh antibody that can affect your unborn baby’s blood cells.
Antibodies are normally useful because they protect you from many common diseases, but in this case, the antibodies can make your baby anemic and complicate your future pregnancies. Fortunately, Rh sensitization does not usually affect the baby in your first pregnancy.
If you are Rh negative and you have not become sensitized to the Rh factor, you should have an injection of Rh immunoglobulin within 72 hours of every delivery, miscarriage, or abortion.
In addition, you may receive an injection of the Rh immunoglobulin at about 28 weeks of pregnancy. These injections help to prevent sensitization and avoid problems in future pregnancies.
If you know you are Rh negative, be sure to tell your health care provider.