Rh factor in pregnancy: When is it a problem?

What are the health issues for pregnant women with Rh negative blood?

- Paul / Minnesota

Answer

Rhesus (Rh) factor refers to a specific antigen in the blood. If your blood lacks the Rh antigen, you are Rh-negative. If your blood has the antigen, you are Rh positive. When the mother is Rh negative and the father is Rh positive, the fetus can inherit the Rh factor from the father. This makes the fetus Rh positive as well.

In such cases, an Rh negative mother may make antibodies to an Rh positive fetus. These antibodies may attack and destroy the fetal red blood cells, leading to hemolytic anemia. However, as long as the mother and her doctor are aware of the blood type, such problems can usually be prevented.

To reduce this risk, an Rh negative pregnant woman receives injections of Rho (D) immune globulin. This protein blocks the recognition of Rh positive cells by the mother's body at the time a pregnant woman is most likely to be exposed to cells from her Rh positive fetus — at about 28 weeks into the pregnancy and immediately after delivery. With these injections, Rh negative women can have safe Rh positive pregnancies.

If a woman is Rh negative, it's important that she report any bleeding she experiences during pregnancy, reminding her doctor of her Rh negative status. The doctor may recommend injections of Rho (D) immune globulin in these circumstances as well.

If a woman develops Rh antibodies, future pregnancies will be closely monitored. If the fetus is found to be anemic during the pregnancy, a transfusion to the fetus through the umbilical cord is possible. Often, early delivery is required. A special type of blood transfusion — called an exchange transfusion — may be performed shortly after birth if destruction of the baby's blood cells continues to be a problem. However, because of the success of Rho (D) immune globulin, such complex treatments are rarely needed.

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