written by: R. Elizabeth C. Kitchen•edited by: Leigh A. Zaykoski•updated: 3/31/2010
The Rhesus factor is what determines whether our blood is classified as positive or negative. Read on the learn more about the genetics of Rhesus factor.
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Rhesus factor, more commonly referred to as Rh factor, is a protein, more commonly an antigen, that exists on a red blood cell's surface. Rhesus factor got its name from experiments that Alexander S. Weiner and Karl Landsteiner conducted in 1937. These experiments involved rabbits that produced an antigen present in many humans' red blood cells when the rabbits were injected with the red blood cells of the Rhesus monkey. This led to the understanding of the genetics of Rhesus factor.
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Categories of Blood
A, B, AB, and O are the four main categories of blood. Each of these blood types is further classified as negative or positive, which is a reference to the blood's Rhesus factor. People who have the antigen in their blood, or Rh factor, are deemed Rh-positive. For example, a person with the A blood type and Rhesus factor in their blood has A-positive blood. It is estimated that more than 85 percent of people throughout the world are Rh-positive. People who do not have the antigen, or are without the Rhesus factor, are Rh-negative. For example, a person with the O blood type and no Rhesus factor in their blood has O-negative blood.
Whether or not a person is Rh positive or Rh negative is really only significant with respect to pregnancies. For example, if an Rh-negative woman gives birth to an Rh-positive child, the child is at risk for developing Rh disease. Only women who are Rh-negative are at risk for giving birth to a child with Rhesus factor disease. For a woman who is Rh-negative to give birth to an Rh-positive child, the childs' father must be Rh-positive. There is a 50 percent chance that a man who is Rh-positive will pass the Rh-positive blood type down to his child.
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How Rhesus Disease Occurs
The genetics of Rhesus factor play a major role in whether a child is born with Rhesus factor. If a child is Rh-positive and the mother is Rh-negative, and the child's blood gets into the mother's bloodstream during pregnancy, labor, or delivery, the mother's immune system may produce antibodies to fight off the child's antigens. These antigens will be seen as foreign by the mother's immune system. The antigens produced by the mother will attack the babys' blood resulting in the red blood cells in the babys' blood breaking down. This can only affect the childs' health and the mother will not experience any adverse health effects. Potential health problems associated with this incompatibility are referred to as Rhesus disease and they include jaundice, heart or brain damage, and anemia. Rh disease can be fatal in severe cases.
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Preventing Rhesus Disease
There are things available to help prevent Rhesus disease. During their first pregnancy, women should be tested to determine whether they are sensitized and Rh-negative. Women who have not been sensitized, but are Rh-negative, can be given an injection of Rh immunoglobulin when they are about seven months pregnant. This injection will help to destroy all antigens in the bloodstream before the mother's immune system has time to create antibodies.
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University of Virginia Health System. (2004). Blood Types in Pregnancy. Retrieved on March 30, 2010 from the University of Virginia Health System: http://healthsystem.virginia.edu/uvahealth/peds_hrnewborn/bloodtyp.cfm