A known risk factor for cerebral palsy, ABO Blood Type Incompatibility results when the blood type of the fetus, or developing child, differs from the blood type of the mother. This can occur if (1) the mother is type O and the fetus is either B, A, or AB, (2) the mother is A and the fetus is B or AB, or (3) the mother is B and the fetus is A or AB.
When incompatibility occurs, the mother creates antibodies to defend against the blood type of the infant. These antibodies cross the placenta and begin destroying the fetus' blood cells. The result is that the fetus develops jaundice, and if untreated, more significant problems can develop such as cerebral palsy.