Hemolysis does not necessarily occur when the mother has type O blood and the child has type A blood. Hemolysis is the mother and child blood type incompatibility caused by homoimmune hemolysis, ABO blood type incompatibility is the most common, Rh blood type incompatibility is less common.ABO hemolysis mainly occurs in the mother O type and the fetus for type A or B, but mother and child ABO blood type incompatibility, only 1/5 happen ABO hemolysis. Among them, 40% to 50% of ABO hemolytic disease occurs in the first child, mostly due to the O-type mothers in the first pregnancy before, has been subjected to nature A or B blood type of various substances stimulation, has produced anti-A or anti-B antibody. Therefore, the mother’s O-type blood child A-type blood does not necessarily occur hemolysis, if the child occurs hemolytic symptoms, need to consult a doctor in time, under the guidance of the doctor for treatment.