Your blood type—such as А, В or AB—contains a factor that determines if it is positive or negative. In the past, Rh-negative women who carried an Rh-positive child faced complicated pregnancies that could result in a very sick baby. Today, most of these problems can be prevented. If you are Rh-negative, you and your doctor need to know it. You will require additional attention during pregnancy and after your baby is born.
If you are Rh-negative and your baby is Rh-positive, if you have had a previous pregnancy, a blood transfusion or have received blood products of some kind, you could become Rh-sensitized (isoimmunized). This could affect the baby.
Isoimmunized. An Rh-negative woman becomes isoimmunized (sensitized) when Rh-positive blood gets into her bloodstream. This can happen with a blood transfusion, the previous birth of an Rh-positive baby, a miscarriage or an ectopic pregnancy.
If you are isoimmunized, certain antibodies are circulating inside your system. They won't harm you, but they can attack the blood of an Rh-positive fetus. Your antibodies can cross the placenta and attack your baby's blood. This can make your baby anemic while it is still inside the uterus. That condition can be very serious.
Preventing problems. Most problems can be prevented with the use of RhoGAM®, which is Rh-immune globulin, a blood product. If you are Rh-negative and pregnant, an injection of RhoGAM is given at 28 weeks of pregnancy to prevent sensitization before delivery. You will be given a second injection of RhoGAM within 72 hours after delivery if your baby is Rh-positive.
If you cannot use blood products for personal, religious or ethical reasons, discuss this with your doctor.
RhoGAM is also used if you have an ectopic pregnancy and are Rh-negative. This also applies to miscarriages and abortions. If you are Rh-negative and have amniocentesis, you will also receive RhoGAM.