Rh Factor Health Article

Rh Factor

An antigen found on the red blood cells of most people. Individuals with the Rh factor are considered as Rh positive, while those without the Rh factor are considered Rh negative.

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

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.