What is the definition or description of: rh sensitization?

Antibody reaction: The rh factor is one of many different markers or antigens on the red blood cell (rbc). Every person is either rh positive or rh negative. An rh negative woman can become 'sensitized' to rh positive red blood cells by a transfusion or at the time of delivery and produce antibodies to rh pos rbc's. That could threaten a future pregnancy. Fortunately, we now have drugs to prevent sensitization.