Vanguard Health Systems has more time to close its $417 million acquisition of Detroit Medical Center.

DMC's board of directors voted Tuesday to extend the companies' definitive purchase agreement from an Oct. 31 deadline to Dec. 31 to allow more time for required regulatory approvals. The Detroit health system's board chairman said in a statement that "government officials have been working diligently, but the complexity and size of the transaction has taken more time than expected."