Rh factor in pregnancy: When is it a problem?

Rhesus (Rh) factor refers to a specific antigen in the blood. Problems can occur when an Rh negative woman is pregnant with an Rh positive baby — which can occur if the father of the child is Rh positive.

Your immune system normally protects against potentially harmful substances (antigens) by making antibodies to help destroy them. An Rh negative woman pregnant with an Rh positive fetus may make antibodies to the Rh positive fetal cells. In a subsequent pregnancy, these antibodies may destroy the fetal red blood cells, leading to serious problems in the fetus.

To reduce this risk, an Rh negative pregnant woman receives injections of Rho (D) immune globulin (RhoGAM). This injection blocks the recognition of Rh positive cells by the mother's body at the times a pregnant woman is most likely to be exposed to cells from her Rh positive baby — at about 28 weeks in the pregnancy and immediately after delivery. With these injections, Rh negative women can have safe Rh positive pregnancies.

If you are Rh negative, it is important to report any bleeding you may experience during pregnancy and remind your doctor of your Rh negative status. He or she may recommend injections of RhoGAM in these circumstances as well.