An incompatibilty of blood types. Blood types are commmonly
characterized by the ABO typing system and the Rh system. An
incompatiblity between the mother and fetus in either of these
systems can result in maternal antibodies crossing the placenta
and destroying fetal red blood cells. The Rh system more often
causes serious problems than the ABO system. Individuals are
either Rh-positive (red blood cells carry the Rh antigen) or Rh-
negative. When a Rh-negative woman is pregnant with a Rh-
positive fetus (Rh-positivity inherited from the father), the
mother can produce antibodies against the Rh portion of the
fetal red blood cells. These antibodies attack the fetal red
blood cells and destroy them. Loss of the fetal red blood cells
causes elevated bilirubin, decreased red blood cell count and
sometimes even heart failure in the fetus. The combination of
these problems can be fatal. There are ways to treat this
problem before the baby is born. More effective than treatment
is prevention of the problems. Women ar