Rh Factor

The danger of Rh disease begins when the mother's Rh negative blood is exposed to the baby's Rh positive blood. This mixing of blood occurs at the time of birth, and after an abortion or miscarriage. It is also apt to happen during prenatal tests like amniocentesis and chorionic villus sampling. More rarely, blood from the mother and fetus may mingle during pregnancy, before birth. When this contact between the two blood types occurs, the mother's body responds by building antibodies to fight the foreign Rh blood protein. The mother's blood is now said to be "sensitized" against Rh factor blood.

Once a mother's blood has become sensitized, her antibodies will attack the blood of any Rh positive fetus that she carries. The antibodies will destroy the fetus's red blood cells. If this happens, the infant will suffer from several serious conditions. It will become anemic, a condition caused by a reduction in red blood cells and marked by weakness and fatigue. Severe anemia can lead to heart failure and death. The breakdown of red blood cells will also cause the formation of a reddish-yellow substance known as bilirubin. An infant with high levels of bilirubin will look yellowish. This is known as Rh disease. Illustration by Hans & Cassidy. Courtesy of Gale Group. jaundice. Brain damage can occur if the bilirubin level gets high enough. The disease caused by Rh incompatibility is called Rh disease, also known as hemolytic disease of the newborn or erythroblastosis fetalis.

Rh disease is usually not a problem during a first pregnancy. This is because the Rh negative mother probably will not become sensitized until her blood mixes with the baby's blood during birth. Her baby will be born before her blood can produce antibodies against the baby's Rh positive blood. Once a mother is sensitized, however, any future babies with Rh positive blood will be at risk for Rh disease.

Since 1968, a vaccine has existed to prevent sensitization from ever occurring. This is the best way to eliminate Rh disease. Available as an injection, the vaccine is called Rh immune globulin (brand name RhoGAM). It blocks the action of the antibodies and prevents the mother's blood from attacking the baby's blood. To be effective, the vaccine must be given any time fetal blood mixes with maternal blood: after birth, abortion, miscarriage, or prenatal tests like amniocentesis and chorionic villus sampling. The vaccine is typically given within 72 hours of any of these events. Since mixing of the blood may occur during the last three months of pregnancy, some health care providers recommend receiving the vaccine at 28 weeks of pregnancy.