If the woman is Rh negative (i.e. her red blood cells do not have the Rh factor), she may detect the fetus' red blood cells as foreign if they do have the Rh factor. This situation can occur if the fetus has inherited the Rh factor from its other parent, thus being Rh positive.
Thus, the Rh-negative mother would produce antibodies against these fetal red blood cells, which she does not recognize as her own, upon contact during pregnancy or delivery.
However, during the first pregnancy with this condition, the antibodies created usually only "sensitize" the mother to the condition. However, it is more common that complications can occur in subsequent pregnancies, if the fetus is also Rh positive, as the amount of antibodies produced would be greater. These antibodies can cross the placental barrier and attack the red blood cells of the fetus.
One of the main consequences would be fetal anemia, which can have different repercussions depending on its severity.
However, these problems can be avoided by administering Rh immunoglobulins to the woman in situations where indicated.
