http://www.healthcaredive.com/news/will-antitrust-concerns-threaten-big-5-consolidation/401480/

Potential consolidation deals among the nation’s major health insurers are sparking antitrust concerns. Among those moves being watched: Anthem going after Cigna; Aetna going after Humana; and UnitedHealth going after Aetna.  The Department of Justice plans to take a hard look if any deals are struck to address questions of whether mergers would suppress competition and present a negative impact to the market.