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Background & Rh Incompatibility
Specific proteins are located on the surface of a person's red blood cells. These proteins uniquely compose one of the four blood types: A, B, AB, and O. Each of these blood types is additionally classified according to the presence of another protein on the red blood cell surface (Rh-positive) or the absence of such protein (Rh-negative). The majority of the population is Rh-positive (approximately 85% Caucasian, 97% African American). These Rh-positive women do not have to worry about Rh incompatibility, only Rh-negative women.
Rh incompatibility occurs when the unborn baby is Rh-positive and the pregnant mother is Rh-negative (Figure 1). The mother's immune system recognizes the baby's blood as foreign (due to the extra protein marker) and forms antibodies to the baby's red blood cells, otherwise known as sensitization (Figure 2).
Occurrence
Rh incompatibility is not usually a problem if it is the mother's first pregnancy since the baby's blood does not typically enter into the mother's bloodstream until she gives birth. However, if the mother ever carries another Rh-positive baby, her immune system will recognize the Rh proteins on the baby's red blood cells as foreign, and cross over into the baby's bloodstream to attack and kill those cells (Figure 3). The following are some situations in which the baby's blood may
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cross the placenta during pregnancy: after amniocentesis or other invasive procedures, during a miscarriage or abortion, during an ectopic pregnancy (pregnancy in the fallopian tube), or if a woman experiences heavy bleeding during pregnancy.
Symptoms
The mother will not typically have any symptoms. The baby will show signs and symptoms of anemia, jaundice (yellowing of the skin), and post-delivery breathing problems.
Diagnosis
Women at risk for Rh incompatibility can be identified with routine blood tests taken at prenatal visits with their physician. These tests include: blood type, Rh type, and antibody screening. If the mother is Rh-negative, the baby's father should also be tested. If the father's blood is Rh-positive, the baby may inherit Rh-positive blood from him; however, if the father's blood is Rh-negative, the infant will be Rh-negative and no Rh incompatibility issues will exist.
Treatment
When a woman with the potential to develop Rh incompatibility is pregnant, physicians administer a series of two Rh immune-globulin shots (i.e. RhoGAM®) during each pregnancy. The first shot is given around the 28th week of pregnancy, and the second shot within 72 hours after giving birth. This Rh immune-globulin acts like a vaccine; the antibodies in the
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shot destroy any red blood cells from the baby that are in the mother's bloodstream. Then the mother's immune system will not make antibodies to the Rh-positive red blood cells.
Rh immune-globulin is a blood product. According to the manufacturer, it should only be administered to adults.
Unfortunately, if a woman has become sensitized (developed antibodies), the Rh immune-globulin shot is not helpful. The woman will remain sensitized, and the effects are usually worse with each subsequent pregnancy. In rare cases if the incompatibility is severe and the baby is in danger, a series of special blood transfusions can be administered. During these exchange transfusions the baby receives Rh-negative blood either while still in utero or after delivery. This stabilizes the baby's red blood cell level and minimizes further damage caused by the mother's circulating Rh antibodies already present in the baby's bloodstream.
*For additional information talk with your physician or pharmacist. You may also find helpful information on this topic by visiting www.rhogam.com/English/Patients/index.aspx or www.rhophylac.com/PatientEducation/education.asp.
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