ABO Hemolytic Disease is a disease caused by ABO blood group incompatibility between mother and child. Most children with ABO Hemolytic Disease have no significant abnormalities other than jaundice. Treatment is usually not required. ABO Hemolytic Disease most often occurs in children born to type O mothers with type A or B blood that is incompatible with their own blood type. Since fetal red blood cells can pass through the placenta and enter the mother’s body with type O blood, causing the mother to produce antibodies against the fetal red blood cell antigens, and the antibodies can be circulated through the placenta to the fetus, which can ultimately lead to the development of ABO Hemolytic Disease in the fetus or the neonate. The severity of symptoms is basically the same as the degree of hemolysis. Most children with ABO hemolytic disease do not have any obvious abnormalities other than jaundice.