How can the Kell and Kidd blood group systems cause hemolytic disease of the newborn?

The Kell and Kidd blood group systems can cause erythroblastosis fetalis—also known as hemolytic disease of the newborn—when there is a blood group incompatibility between a mother and her fetus.12

This condition occurs when a mother develops IgG antibodies against specific antigens present on the fetal red blood cells. These antibody molecules are capable of crossing the placenta and entering the fetal circulation, where they bind to and destroy the fetal red cells.1

The Kell and Kidd systems were historically identified in part because researchers discovered infants suffering from this disease even when the mother and child were compatible within the Rh blood group system. In the case of the Kidd blood group system, antibodies that bind to Kidd proteins can lead to this destruction of fetal red cells. Similarly, the Kell blood group system is recognized as a cause of such incompatibilities. When this occurs, the newborn may be anemic at birth and require medical intervention, such as transfusion with antigen-negative red cells.231