UnitedHealth's cautious approach to offering plans on the Affordable Care Act marketplaces has paid off for the nation's largest insurer, according to stock analysis firm Trefis. While UnitedHealth participated in just four exchanges during the first open enrollment period--a move that led it to lose market share in 2014--the insurer expanded to 24 exchanges during the second open enrollment period, increasing its total enrollments from 5.1 million in 2014 to 7.9 million in 2015. Going forward, the article suggests that UnitedHealth should focus on states such as California, Texas and Florida that have large-scale enrollments, as well as states with fast-growing markets such as North Dakota, Oklahoma, Nebraska, South Carolina, Virginia and Arizona. Beyond its health plan offerings, UnitedHealth also has had success with its Optum business, which grew 15 percent year-over-year, the company said when it reported its second-quarter earnings in July. Article