Rh factor

Rh factor

noun \ˈär-ˈāch-\

Definition of RH FACTOR

: a genetically determined protein on the red blood cells of some people that is one of the substances used to classify human blood as to compatibility for transfusion and that when present in a fetus but not in the mother causes a serious immunogenic reaction in which the mother produces antibodies that cross the placenta and attack the red blood cells of the fetus—called also rhesus factor