Which pregnant client is most at risk for ABO incompatibility?

A. When the mother is blood type A and the fetus is also blood type A, the red blood cell antigens are the same. Because the mother does not have antibodies against her own blood type, there is no risk for ABO incompatibility in this situation. B. A mother with blood type AB has both A and B antigens and therefore does not produce anti-A or anti-B antibodies. Since ABO incompatibility depends on maternal antibodies attacking fetal red blood cells, this combination does not place the fetus at risk. C. If both the mother and fetus are blood type B, the maternal immune system recognizes the fetal red blood cells as “self.” No antibody-mediated hemolysis occurs, so ABO incompatibility is not a concern. D. A mother with blood type O is at the greatest risk for ABO incompatibility, especially when the fetus has blood type A or B. Mothers with type O blood naturally have both anti-A and anti-B IgG antibodies. These antibodies can cross the placenta during pregnancy and attack fetal red blood cells, leading to hemolysis. This can result in conditions such as neonatal jaundice and, in more severe cases, anemia. Therefore, this maternal–fetal blood type combination presents the highest risk for ABO incompatibility.