Rh factor, like the blood types A, B, and O, is inherited from one's parents. Through a simple blood test, blood type and the presence of the Rh factor can be determined. About 85% of white Americans and 95% of African Americans are Rh positive. A person's state of health is not affected by the presence or absence of Rh factor.
Importance of the Rh factor
The Rh factor, a blood protein, plays a critical role in some pregnancies. If an Rh negative woman is pregnant with a fetus who is Rh positive, her body will produce antibodies against the fetus's blood. This can cause Rh disease, also known as hemolytic disease of the newborn, or erythroblastosis fetalis, in the baby. In severe cases, Rh disease leads to brain damage and even death.
Rh factor is important only during a pregnancy in which an Rh negative woman is carrying an Rh positive fetus . This can occur when an Rh negative woman conceives a baby with an Rh positive man. The gene for Rh positive blood is dominant over the gene for Rh negative blood, so their baby will be Rh positive. If the Rh positive father also carries the gene for Rh negative blood, his children have a 50% chance of inheriting Rh negative blood and a 50% chance of inheriting Rh positive blood. If both parents are Rh negative, their offspring will always be Rh negative. In order to protect their future children from Rh disease, all women of childbearing age should know their Rh status before becoming pregnant.
Rh factor in pregnancy
The conditions allowing for Rh disease are established when the blood of an Rh negative mother is exposed to the Rh positive blood of her first baby, prompting the mother's immune system to build up antibodies to fight the foreign blood protein. Since this exposure usually occurs at birth, the first child is generally unaffected, but any fetus the mother carries afterward will develop Rh disease unless preventative measures are taken. Mixing of blood also occurs during an abortion or miscarriage and results in the same sensitization. Certain prenatal tests, such as amniocentesis and chorionic villi sampling, can also result in maternal exposure to fetal blood.
The attack of a mother's antibodies on the red blood cells of her Rh positive fetus results in several serious conditions. The first, anemia , refers to a reduction in red blood cells and is marked by weakness and fatigue. Another consequence is the buildup of a reddish yellow fluid called bilirubin, which in turn causes jaundice . If the bilirubin level gets high enough, brain damage can result. The most severe form of Rh disease, called hydrops fetalis, is marked by profound anemia and edema. Infants with hydrops fetalis are usually stillborn or only survive a few hours after birth.
Treatment for Rh disease
Since 1968 a vaccine has existed which prevents sensitization from even occurring. The vaccine is considered the best way to eliminate Rh disease because it prevents the mother's body from making antibodies against the fetus's blood. The vaccine, called Rh immune globulin (RhoGAM), is available by injection. RhoGAM blocks the action of the antibodies and prevents the mother's antibodies 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.
If a woman has become sensitized during a previous pregnancy, she can still take steps to prevent future babies who are Rh positive from developing Rh disease. Unfortunately, once the harmful antibodies are in a woman's blood, they cannot be removed.
A pregnant woman who has already been sensitized from a previous pregnancy should be carefully monitored throughout her pregnancy for the level of antibodies in her blood. As long as the antibody levels remain relatively low, no problem exists. However, if those levels rise, the fetus will need special attention. High antibody levels indicate that the fetus's red blood cells are being attacked and destroyed.
In these circumstances, the fetus will need a blood transfusion while it is still in the uterus. Two or three transfusions may be necessary before the baby is born. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early, either through an induced birth or cesarean section. The baby will then receive a transfusion after birth.
Eliminating Rh disease
Until the introduction of RhoGAM, Rh disease could not be prevented. Prior to widespread use of the vaccine in the early 1970s, researchers reported that approximately 45 babies per 10,000 births developed Rh disease yearly. The number of newborns with Rh disease has dropped dramatically ever since the introduction of the vaccine; about 10 per 10,000 in the early 1990s. The prevention of Rh disease is one of the triumphs of modern medicine.
Nevertheless, a relatively high number of newborns with Rh disease are still delivered each year in the United States. Clearly, the disease is not completely eradicated. Further steps must be taken since this is a preventable disease. The majority of Rh disease cases of are the result of women not receiving the vaccine at the appropriate time. Poor women, particularly those without health insurance, are the ones most at risk for inadequate prenatal care. Older women may have become sensitized before the vaccine was available. Foreign-born women may not have had access to the vaccine. With further diligence, health care providers hope to eradicate Rh disease.
Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.