Hemolytic disease is suspected in a mother's second newborn. Which factor is important in understanding how this could develop?

A) The mother's first child was Rh positive.
B) The mother is Rh positive.
C) Both parents have type O blood.
D) RhIG (RhoGAM) was given to the mother during her first pregnancy.

Hemolytic disease of the newborn results from an abnormally rapid rate of red blood cell (RBC) destruction. The major causes of this are Rh and maternal-fetal ABO incompatibility. If an Rh-negative mother has previously been exposed to Rh-positive blood through pregnancy or blood transfusion, antibodies to this blood group antigen may develop so that she is isoimmunized. With further exposure to Rh, the maternal antibodies will agglutinate with the red cells of the fetus who has the antigen and destroy the cells. Hemolytic disease is also caused by ABO incompatibilities. Blood type is the important consideration. If both parents are type O blood, ABO incompatibility would not be a possibility. The mother should have received Rh?(D) immune globulin to prevent antibody development after the first pregnancy.