Rh Factor

Definition - What does Rh Factor mean?

Rh factor is an antigen that classifies blood types in addition to type A, B, and O. Rh is genetically inherited. Rh-positive means the protein is present on the surface of red blood cells. Occasionally pregnant woman can have Rh incompatibility with their fetus leading to complications.

If the mother is Rh-negative with a Rh-positive fetus she can become Rh sensitized (produce antibodies against the Rh factor). These antibodies have the potential to attack and kill fetal red blood cells. This results in hemolytic anemia (lack of enough oxygen supplying red blood cells) which may cause miscarriage.

FertilitySmarts explains Rh Factor

During pregnancy, the mother and fetus do not share blood systems. Rh sensitization becomes a problem whenever even a small amount of blood crosses the placenta during pregnancy, labor or birth, amniocentesis or chorionic villus sampling (procedures requiring a small needle insertion near the fetus), or any trauma or bleeding that may occur. Often sensitization occurs during the first pregnancy without causing problems until a subsequent pregnancy. Antibodies can still develop during a pregnancy even if it is not carried to term.

Woman are blood tested for Rh antigen during prenatal care to determine risk. Rh negative women who are not sensitized can receive RH immunoglobulin (RhIg). RhIg targets Rh positive blood cells and prevents the production of antibodies against them ,thus preventing hemolytic anemia later.

Women may be antibody screened to determine sensitization. Rh sensitized woman pregnant with a Rh-positive fetus are monitored routinely for development of fetal anemia. They may require early labor induction or blood transfusion. RhIg is not effective in already sensitized women.

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