Rh factor can complicate pregnancy
Dear Dr. Roach: My wife is Rh negative, and I am Rh positive. Our baby (fetus) is positive. I am worried about my wife and my baby. Is this dangerous? What can be done? This is her second pregnancy.
H.D.
Answer: Blood types are complicated. A simple version that’s familiar is the A, B and O types. An additional layer to that is the RhD factor. It’s the RhD factor that has the greatest potential to cause a dangerous condition called hemolytic disease of the fetus and newborn. Babies are at risk for HDFN when the mother is RhD-positive and the father is RhD-negative. Since we carry two genes for the RhD factor, not all babies will be RhD-positive, even if one parent is. When the developing fetus is also positive and the mother is negative, intervention is necessary to reduce the risk of HDFN.
In the first pregnancy, the risk of HDFN is low, since the mother does not usually have antibodies against the RhD factor. However, during birth, there is often exchange of fetal blood with maternal blood, which causes the mother to begin making antibodies against the RhD factor. It is also possible for the mother to begin making antibodies during the pregnancy due to small amounts of bleeding across the placenta. Most cases of HDFN can be prevented by giving the mother anti-D immune globulin immediately after delivery. This prevents her from making antibodies to RhD factor. Your blood type and wife’s blood type should have been known and the medication given her during her first pregnancy.
Not all cases can be prevented, and so mothers in your wife’s situation are monitored for development of these anti-D antibodies. If the mother develops high amounts of antibodies (as measured by a blood test) during pregnancy, then the developing fetus is monitored carefully for signs that the maternal antibodies are destroying the developing fetus’ blood cells. If there are signs of fetal distress, the fetus may need to be treated with transfusion of RhD-negative blood.
Less than half of all pregnancies where the mother has developed antibodies to RhD develop problems bad enough to be treated, so there is a very good chance she will have no problems.