When Rh-negative pregnant women are pregnant with Rh-positive fetus, a small amount of red blood cells or D antigen of Rh-positive fetus can enter the mother, making the mother produce immune antibodies. This antibody can enter the fetal blood through the placenta, causing hemolysis of fetal red blood cells, hemolytic anemia of newborns and even fetal death in severe cases.
There is an exception, that is, if both parents are Rh-negative, then their children will also be Rh-negative, and this fetus will not be at risk of Rh hemolysis. However, if both parties are RH-negative, then a child who is RH-positive should not have a second child.
Generally speaking, Rh hemolysis is earlier and more serious than ABO hemolysis, Rh hemolysis generally occurs in the second child, and ABO hemolysis can occur in the first child. Neonatal hemolytic disease is closely related to genetic factors, so the incidence of pregnancy is higher and the symptoms are more serious. Because under normal circumstances, only at the end of pregnancy or delivery will enough fetal red blood cells enter the mother, and the antibody concentration in the mother's blood is gradually increasing, so when the Rh-negative mother is pregnant with the first Rh-positive fetus, neonatal hemolysis rarely occurs. The situation of the second pregnancy is somewhat different, because the possibility of fetal hemolysis will increase when pregnant with a second child, so it is necessary to strengthen monitoring and inject immunoglobulin if necessary.
One thing to emphasize is that Rh-negative women should try to avoid multiple pregnancies and abortions, because the more pregnancies, the more serious the mother's sensitization, which will increase the risk of fetal hemolysis and damage the mother.