O-positive blood type means that the human body’s ABO blood type is O blood and Rh blood type is Rh-positive, because there are many kinds of blood type systems in the human body, and the ones that are widely used in clinical practice are ABO blood type system and Rh blood type system, especially Rh blood type system, which is of great importance in human blood transfusion and obstetrics. Because an Rh-negative person can only receive Rh-negative blood in a clinical transfusion, if Rh-positive blood is transfused, a serious hemolytic reaction will occur. By the same token, an Rh-negative mother who gives birth to her first child, who is Rh-positive, is likely to have neonatal hemolysis when that mother gives birth to her second child. This is because since there are very few Rh-negative people, the pregnant woman is likely to have anti-Rh-positive antibodies in her body, and when she gives birth to her second child, these antibodies will enter the fetus and produce neonatal hemolysis.