Rhesus (or Rh) factor is a key component in blood typing. The Rh antigen was first discovered in Rhesus monkeys by Karl Landsteiner and Alexander Wiener in the 1940s. Humans with this antigen require special treatment during pregnancy and blood transfusion.
Rh factor is identified through a simple blood test. Rh proteins discovered in the blood indicate an Rh-positive blood type. Lack of Rh proteins suggests an Rh-negative blood type.
Palomar College of California's website states that only one in 1,000 Rh-negative babies are born annually in the United States. Rh-negative blood type is most prevalent in European countries; 13 per cent of all European babies are Rh negative.
Rh antibody tests are conducted during the first prenatal visit. An Rh-negative person carrying an Rh-positive baby will receive a Rh immunoglobulin (RhIg) to prevent antibodies from attacking the foetus.
Rh-negative people can only receive Rh-negative blood and blood products. An Rh-negative person who receives the incorrect blood may develop anti-Rh agglutinins. This causes the body to destroy red blood cells and is potentially fatal.
The demand for Rh-negative blood is high and supply is low. This is due to the rarity of Rh-negative people.