Rh Testing

Congratulations! You're pregnant. Along with the joy of pregnancy, comes a list of tests that are required to ascertain the safety of your pregnancy and to indicate any precautions that might be needed to ensure that your pregnancy is concluded safely. One of these tests will determine your Rh factor.
Human blood is classified, or typed, according to the presence or absence of certain markers (called antigens) on the surface of red blood cells. Rhesus (Rh) factor is a type of antigen present on the surface of red blood cells. If you have an Rh factor, you are Rh-positive. If you don't, you are Rh-negative. The majority of people are Rh-positive. Your Rh factor is also related to your blood type. For example, if you are blood type O-, you are blood type O with a negative Rh. If you are A+, then you are blood type A and Rh-positive.
The main concern is usually when the pregnant woman is Rh-negative. This will require the immediate testing of the father. If he is also Rh-negative, no precautions will be necessary. However, if he is Rh-positive, the baby will most likely be Rh-positive, and problems may occur when an Rh-negative pregnant woman is carrying an Rh-positive fetus. This is referred to as Rh incompatibility. Since the immune system normally protects against harmful substances, when foreign bodies enter your system your body develops antibodies to destroy them. If you are Rh-negative and you are exposed to Rh-positive blood your body might develop antibodies to help destroy Rh-positive blood at the next encounter with it.
During the first pregnancy, the mother and the fetus should be safe. However, during the delivery, or in the case of a miscarriage, the woman becomes exposed to Rh-positive blood and will most likely develop antibodies to them. In subsequent pregnancies these antibodies might cross the placenta destroying the fetus' red blood cells causing anemia (low iron levels) or heart failure, hence requiring special care during pregnancy. This might also lead to the death of an Rh-positive baby.
Although there should be no risk during a first pregnancy, "Ideally, it is safer for the mother to perform the Indirect Coomb's test which measures the level of antibodies in the body in case the mother had a previous miscarriage (at times the mother might not know of a previous miscarriage), or a blood transfusion that might have exposed her to Rh-positive blood that might not be documented," explains Dr. Mona Aboul Ghar, lecturer of obstetrics and gynecology at Cairo University.
To reduce risks of Rh incompatibility, an Rh-negative pregnant woman receives injections of Rh (anti-D) immune globulin. The injections are given at about 28 weeks in the pregnancy and immediately after delivery. With these injections, Rh-negative women can have safe Rh-positive pregnancies.