Rh factor is a molecule on the surface of RBC's(Red Blood Corpuscles) in some people. It is termed as Rh positive if RBC's have the Rh factor and Rh-negative if they do not. Complications can occur if the fetus's Rh-positive blood enters the mother's bloodstream. This results in the mother's immune system to recognize the fetus's RBC's as foreign and produce antibodies against it, called Rh antibodies, to destroy Rh-positive blood cells. The production of these antibodies is called Rh sensitization.

Rh sensitization is unlikely in first pregnancy because there would not be significant amount of the fetus's blood entering the mother's bloodstream till delivery. Hence the fetus or the newborn rarely has any problems. However, a woman becomes sensitized during delivery. Once she is sensitized, roblems are more likely with each subsequent pregnancy as the woman produces Rh antibodies earlier and in larger amounts if the fetus is Rh positive.

If Rh antibodies cross the placenta to the fetus, fetus's RBC's get destroyed. If the destruction rate is more than the production rate then the fetus can develop anemia. Such destruction is called hemolytic disease of the fetus (erythroblastosis fetalis) or of the newborn. In severe cases, the fetus may die or miscarriage can occur.

Diagnosis

Women are generally screened in their first visit to determine whether they have Rh-positive or Rh-negative blood. Father's blood type is also determined. If he has Rh positive blood then there is a risk of sensitization. In such cases, blood of pregnant women is screened for Rh antibodies periodically during the pregnancy. Pregnancy can continue as long as the antibodies are not detected. In case if the antibodies are detected, steps can be taken to protect the fetus depending on the antibody level. Doppler ultrasonography is done periodically to assess blood circulation in fetal brain. If an abnormality is detected then one of the following 2 procedures is done for further evaluation:

1. Amniocentesis
2. Percutaneous umbilical blood sampling

Prophylaxis

As a precaution, women who have Rh-negative blood are given an injection of Rh antibodies at 28 weeks of pregnancy and within 72 hours after delivery of a baby who has Rh-positive blood, even after a miscarriage or an abortion. It is also given after any episode of vaginal bleeding, amniocentesis or chorionic villus sampling. The antibodies given are called Rh0(D) immune globulin. This treatment destroys any RBC's from the baby that may have entered the woman's bloodstream. This is done to ensure that the RBC's from the baby to trigger the production of antibodies and ensure that subsequent pregnancies are usually not complicated.

Treatment

If anemia is suspected, the fetus is given blood transfusion. Usually addition transfusions are indicated till the fetus is mature enough for delivery.

After delivery the newborn may need additional transfusions. Sometimes no transfusions are needed till birth.