WHY IT MATTERS: UnitedHealth is the largest U.S. health insurer and the first to announce earnings every quarter. Many analysts and investors see it as a bellwether for the managed care sector.Aetna Inc., the third largest insurer, reports results on Oct. 25, followed by Cigna Corp. on Nov. 1 and Humana Inc. on Nov. 5. The second-largest insurer, WellPoint Inc., then will wrap up reporting for the five biggest managed care companies when it releases results Nov. 7. WHAT'S EXPECTED: Analysts surveyed by FactSet now expect, on average, earnings of $1.34 per share on $27.58 billion in revenue. LAST YEAR'S QUARTER: UnitedHealth reported earnings of $1.27 billion, or $1.17 per share, on $25.28 billion in revenue for 2011's third quarter. The earnings beat analyst expectations, like UnitedHealth typically does. But the insurer's stock slipped the day it reported results, as it also warned investors of challenges like high unemployment rates and growing health care use that were expected to squeeze the company's 2012 performance.