Rh incompatibility occurs when the mother's blood is Rh-negative and the baby's blood is Rh-positive.
At your first medical visit, blood is drawn to determine your blood type and Rh factor. You are either Rh-positive (as approximately 85 percent of Caucasians and a slightly higher percentage of African Americans and Asians are) or you are Rh-negative. This is important to determine because if you are Rh-negative and your partner is Rhpositive, the fetus might have Rh-positive blood like the father. When this happens, the fetus's blood is different from the mother's, causing Rh incompatibility. The mother's blood might respond as if it were allergic to the fetus's blood by making antibodies against the fetus's blood. This is called sensitization. If the antibodies from the mother's blood cross the placenta into the fetus's blood, the antibodies attack, breaking down the fetus's red blood cells and causing anemia. This is a very serious condition known as erythroblastosis fetalis. It can cause serious illness or even death in the fetus or newborn.
Fortunately, sensitization to the Rh factor can be prevented if the mother does not become sensitized in the first place. To do this, an Rh-negative woman is given Rh immunoglobulin (Rhlg) near the 28th week of pregnancy to prevent her from producing antibodies. If her baby is Rh-positive, the mother will be given another dose shortly after delivery. Repeat doses of Rhlg are given with each pregnancy and birth of an Rh-positive baby. This course of detection and prevention makes the deadly erythroblastosis fetalis completely preventable today.
Not all pregnancies are smooth sailing. If you find yourself in a problem pregnancy, be sure to get good medical care and follow your doctor's instructions. As medical science improves, more and more previously fatal or permanently damaging conditions have become controllable and even harmless. That's the good news.