Rhogam is necessary for pregnant woman that are lacking the ‘D antigen’ on their red blood cells. This is what is known as being RH-negative. ‘D-antigen is an inherited factor that people acquire from their parents, such as hair and eye color. Some people do not receive this. There are problems that may arise for rh-negative pregnant woman, and rhogam is needed to prevent. The fetus carries antibodies that may leak into the mother’s bloodstream, if the babies rh-factor is positive, the mother’s negative ones produce antibodies to fight them. Rho-gam injected into the muscle of the mother, will protect against any rh-positive red blood cells that may enter the mother’s system.