Children born to couples with type B blood may be type B and type O. According to the law of heredity, there is a 15/16 chance of having a child with type B blood and only a 1/16 chance of having a child with type O blood, and it is not possible to have a child with type A or AB blood. There are many different human blood group systems, but the most clinically significant are the ABO blood group system and the Rh blood group system; Rh hemolysis has the most serious consequences and the fetus may develop edema or even die during pregnancy due to hemolysis. It is important to have a clear picture of the blood type. If there is no previous history of blood contact, hemolysis will not occur in the first pregnancy, but a second pregnancy needs to be taken seriously, especially for the Rh blood group system, to have the blood group immune antibodies measured and try to plan the pregnancy six months after the antibodies disappear.