[Erythrocyte isoantigens of the Rh (Rhesus) blood group system, the most complex of all human blood groups, because the genes differ by determining a different number of the over thirty antigens thus far described and do so with remarkably different quality. The major antigen Rh or D is the most common cause of erythroblastosis fetalis. ( MSH )] (UMLS (CSP) C0035406) =Body System ;