Less Common Form: Rh Incompatibility

     The less common form of Erythroblastosis fetalis is Rh incompatibility.  This is similar to what happens in ABO incompatibility, but the mother's blood type is Rh-negative, while the fetus' blood type is Rh-positive.  As in the other form, the mother's antigens produces antibodies as an immune system reaction to the foreign blood type of the fetus, thus attempting to expel the fetus from the mother's body.  The anti-Rh antibodies produced by the mother would then cross into placental membrane and into the fetus' bloodstream, where they would result in the increased production of bilirubin.  Once again, as in ABO incompatibility, increased levels of bilirubin in a newborn could eventually lead to newborn jaundice.
     However, unless the mother has had previous pregnancies that had ended in either miscarriages or abortions, the firstborns are not affected by this disease.  It seems that time is needed for the mother's body to produce the anti-Rh antibodies sensitive enough to attack the fetus' Rh-positive blood type.  Following pregnancies with fetal blood type of Rh-positive would induce Rh incompatibility.

-Teresa