UnitedHealth Group (UNH), the nation's largest health insurer, will be the first HMO to report fourth-quarter earnings on Thursday before the market opens. The report comes in the wake of the fiscal cliff deal that averted many major tax increases, and put off the hard question of how to cut spending until March. The agreement was seen as mildly positive for insurers who don't have to deal with across-the-board spending cuts for now. The 23