Rh factor is an inherited trait that does not affect health but sometimes affects pregnancies of Rh-negative mothers carrying Rh-positive babies, states Mayo Clinic. Rh factor is a protein located on the red blood cells. Individuals with the protein are Rh positive; those without it are Rh negative.
There is a chance of Rh incompatibility when the mother of a child is Rh negative and the father is Rh positive although such problems are rare during a first pregnancy, according to the American Congress of Obstetricians and Gynecologists. If the baby's blood comes in contact with the mother's, the mother develops Rh sensitivity as her body produces antibodies against the Rh protein. In subsequent pregnancies with Rh-positive babies, the antibodies cross the placenta, where they attack and destroy the fetus's red blood cells. This leads to fetal hemolytic anemia, which is sometimes fatal to the developing child.
If a woman is at risk for developing Rh incompatibility, the National Heart, Lung, and Blood Institute recommends she receive an Rh immune globulin injection. The injection prevents her body from developing the antibody, but it cannot reverse incompatibility once it develops. The woman should have this immunization with each pregnancy, miscarriage or other event that exposes her to Rh-positive fetal blood.