Opposites may attract, but when it comes to certain proteins on red blood cells, a difference between Mom's and Dad’s may cause trouble for Mom's immune system. As part of pre-conception testing while you’re trying to conceive, your doctor will likely order a blood test to determine your and your partner’s Rh factor status. This antigen is called the Rh, since the initial research was done with Rhesus monkeys. Although the Rh blood group system consists of several antigens (e.g, D, C, c, E, e), the D antigen is the most immunogenic and relevant for mother-baby mismatches in pregnancy. Therefore, Rh incompatibility, more often than not, refers to the incompatibility of Rh-D. If you have D-antigen-type red blood cells, you’re “Rh-positive.” If you don’t, you’re “Rh-negative." It’s important to note that mismatches other than Rh-D may require treatment that is different from that for Rh-D itself.
When an Rh-negative mother carries an Rh-positive fetus (a baby who inherited the Rh factor from the father), the mother’s immune system may become sensitized to the foreign protein now on the baby’s red blood cells. The mother’s immune system, now sensitized, makes antibodies, causing her immune system to destroy fetal red blood cells. This can lead to a dangerous anemia called Rh disease, a major cause of fetal death.
If you are an Rh-negative mother in this situation, your doctor would give you a shot containing Rh-immunoglobulin (Rhlg) to prevent sensitization of your immune system either during pregnancy and/or shortly after the baby is born. It is sometimes given as a preventive measure during pregnancy if any bleeding occurs that could expose the mother to fetal Rh factor.
The first pregnancy with an Rh-positive baby may go smoothly, but the next pregnancy may not, as the mother’s immune system sensitizes further. Events during an earlier pregnancy, such as a miscarriage, induced abortion, ectopic pregnancy, blood transfusion, amniocentesis, or chorionic villus sampling procedures, can provide an opportunity for blood mingling between fetus and mother and could also result in sensitization.
Of course, not everyone finds themselves with this challenge when they’re trying to conceive. Even if you do, your doctor can catch this situation while you’re trying to conceive with the help of pre-conception testing and manage it to avoid complications.