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| |    Rh Negative Implications for Pregnancy by Marjorie Greenfield, M.D. reviewed by Laura Jana, M.D., F.A.A.P. Do you know your blood type? Because blood type can be an important factor in a healthy pregnancy, it will be checked at your first prenatal visit. What your blood type means Blood type is based on particular molecules (called antigens) that sit on the surface of red blood cells. People either have A antigens (type A blood), B antigens (type B), both (type AB) or neither (type O) on their red blood cells. When it comes to Rh factor, some people have the antigen (Rh-positive) and some people don't (Rh-negative.) In other words, your blood type identifies which antigens you have from each group. Rh sensitization is preventable During pregnancy, Rh-negative is the only one of these blood groups that can cause a problem. It turns out that an Rh-negative mother can make antibodies (part of her immune system's response to invaders) against Rh-positive blood cells, even against those of her own baby. This is called Rh sensitization. These antibodies have the potential to cross the placenta and attack the fetus' red blood cells, which in turn can cause low blood count (anemia), congestive heart failure, and even fetal death. This is called hemolytic disease. Fortunately, Rh sensitization is preventable with a medicine called Rh immunoglobulin (RhIg, or Rhogam™.) Since the development of RhIg, in 1968, we have seen fewer and fewer mothers who are Rh sensitized. How Rh immunoglobulin works An Rh-negative mother will develop antibodies against Rh-positive blood cells (become sensitized) only if fetal blood crosses the placenta and enters her bloodstream. Her immune system then "sees" these cells, identifies them as foreign, and mounts an immune response. The injection of Rh immunoglobulin blocks the mother's immune system from seeing the fetal cells, if they do happen to get into her bloodstream, so she will not become sensitized and make antibodies. Who needs to take Rh immunoglobulin? RhIg is given to all Rh-negative women whose fetuses might be Rh-positive. The fetus may be Rh-positive if its father is Rh-positive. If both parents are Rh-negative, they can only have Rh-negative offspring. When is Rh immunoglobulin given? RhIg is given at times during the pregnancy when there is some likelihood of Rh-positive fetal blood getting into the mother's bloodstream. This includes
The baby's blood type is checked at birth, using blood obtained from the umbilical cord. If the baby turns out to be Rh-negative as well, the dose of RhIG usually given at delivery is not necessary. What happens when an Rh-negative mother becomes sensitized? Fortunately, it is now quite rare for an Rh-negative woman to get sensitized. If a woman does develop antibodies against Rh-positive cells, it will be detected in routine pregnancy blood-work. Rh sensitization usually doesn't hurt the baby in the first pregnancy, because the mom can't make enough antibodies to cause severe problems. But the next pregnancy, and any that follow, can become very complicated if that fetus is Rh positive. If possible, women who become Rh sensitized should get their prenatal care from a high-risk obstetrical specialist (perinatologist.)
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