Maternal-infant blood group mismatch is a type of blood group antibody that is produced in the mother due to a mother-child blood group mismatch with the fetal blood group antigen. This antibody enters the fetus through the placenta and causes homozygous immune hemolysis, commonly between the RH blood group system and the ABO blood group system. Other causes of hemolysis in the neonatal period are defects in red blood cell enzymes or red blood cell membranes, all of which have proprietary terms. Hemolysis with only blood group incompatibility is called neonatal hemolysis and is usually caused by RH blood group incompatibility between the mother and the fetus. Its development is determined by both parents of the fetus. If the fetus inherits blood group antigens from the father that the mother does not have, then the fetal red blood cells enter the mother, causing the mother to produce the corresponding antibodies, which enter the fetus through the placenta, resulting in an antigen-antibody immune reaction and the symptoms of hemolysis.