State health regulators in Illinois yesterday approved a certification that will allow a proposed affiliation between Des Moines-based Iowa Health System and Methodist Health Services Corp. (MHSC) in Peoria, Ill., to move forward. With the approval of the certificate of exemption by the Illinois Health Facilities and Services Review Board, MHSC will be allowed to operate as the eighth senior affiliate of Iowa Health System upon the closing of the transaction. MHSC operates 37 clinical sites in Illinois, including a 329-bed hospital and a school of nursing. In addition to this agreement, Iowa Health System has affiliation agreements with 25 hospitals in Iowa and Illinois, including 14 major affiliate hospitals in seven regions in the two states and 11 rural hospitals.