Rh blood typing determines the presence (+) or absence (–) of the Rh antigen (also called the Rh factor). If your red blood cells: · Contain the Rh antigen, your blood is Rh-positive. · Do not contain the Rh antigen, your blood is Rh-negative. · Contain the A and Rh antigens, your blood type is A-positive (A+). If your blood contains the B antigen but not the Rh antigen, your blood type is B-negative (B–). Rh blood typing is especially important for pregnant women. A potential problem arises when a woman who has Rh-negative blood becomes pregnant with a fetus that has Rh-positive blood. This is called Rh incompatibility. If the blood of an Rh-positive fetus mixes with the blood of an Rh-negative woman during pregnancy or delivery, the mother's immune system produces antibodies. This antibody response is called Rh sensitization and, depending on when it occurs, can destroy the fetus's red blood cells.