About the Rh Factor
People with different blood types have proteins specific to that blood type on the surfaces of their red blood cells (RBCs). There are four blood types — A, B, AB, and O.
Each of the four blood types is further classified based on the presence of another protein on the surface of RBCs that indicates the Rh factor. If you carry this protein, you are Rh positive. If you don’t carry the protein, you are Rh negative.
Most people — about 85% — are Rh positive. But if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for a baby to have a health problem. The baby growing inside the Rh-negative mother may have Rh-positive blood, inherited from the father. Approximately half of the children born to an Rh-negative mother and Rh-positive father will be Rh positive.
Rh incompatibility usually isn’t a problem if it’s the mother’s first pregnancy because, unless there’s some sort of abnormality, the fetus’s blood does not normally enter the mother’s circulatory system during the course of the pregnancy.
However, during delivery, the mother’s and baby’s blood can intermingle. If this happens, the mother’s body recognizes the Rh protein as a foreign substance and might begin making antibodies (protein molecules in the immune system that recognize, and later work to destroy, foreign substances) against the Rh proteins.
Other ways Rh-negative pregnant women can be exposed to the Rh protein that might cause antibody production include blood transfusions with Rh-positive blood, miscarriage, and ectopic pregnancy.
Rh antibodies are harmless until the mother’s second or later pregnancies. If she is ever carrying another Rh-positive child, her Rh antibodies will recognize the Rh proteins on the surface of the baby’s blood cells as foreign, and pass into the baby’s bloodstream and attack those cells. This can lead to swelling and rupture of the baby’s RBCs. A baby’s blood count can get dangerously low when this condition, known as hemolytic or Rh disease of the newborn, happens.
a child with Rhesus-negative blood — more commonly called Rh-negative blood — lacks the Rh-factor, a protein located on the surface of red blood cells, according to the American Pregnancy Association. People with this protein have Rh-positive blood, while those without it have Rh-negative blood. But having Rh-negative blood is not a disorder. The Tech Museum of Innovation reports that there is some scientific evidence indicating that those who are Rh-negative may have greater protection against some conditions. However, a woman with Rh-negative blood may experience potentially serious complications during pregnancy if she does not receive prompt medical attention before the baby’s birth.
For a child to have Rh-negative blood, he needs to have inherited two Rh-negative genes: one from his father and one from his mother. According to the Lucile Packard Children’s Hospital at Stanford, a couple can have a child that lacks the Rh-factor only if both are Rh-negative or if both carry one recessive Rh-negative gene. People with any of the major blood types — A, B, O or AB — can be born Rh-negative. According to the American Pregnancy Association, approximately 15 percent of the population has Rh-negative blood.
Impact on Health
A child who has Rh-negative blood will not suffer from health problems directly caused by her lack of the Rh-factor, assures the March of Dimes. Having this blood type is simply a trait, similar to having brown hair or freckles. The Tech Museum of Innovation, which is supported by the Stanford School of Medicine’s Department of Genetics, points out that those who have Rh-negative blood appear to have a higher resistance to the deadly parasite Toxoplasma than Rh-positive people. Geneticists theorize that Rh-negative blood may be an adaptation that has evolved to help protect against parasites and viruses, although more research is needed.
The only danger associated with Rh-negative blood is Rh disease, a condition that occurs when a woman with Rh-negative blood conceives a child who is Rh-positive because the child has inherited the dominant Rh-positive gene from his father.