INDIANAPOLIS (AP) — UnitedHealth Group Inc.'s fourth-quarter net income jumped 20 percent and trumped Wall Street expectations, but the insurer left its 2012 earnings forecast unchanged as it saw signs of health care use starting to pick back up.

The Minnetonka, Minn., company said Thursday it earned $1.26 billion, or $1.17 per share, in the three months that ended Dec. 31. That's up from $1.04 billion, or 94 cents per share, in the same quarter last year.

Revenue grew 8 percent to $25.92 billion.

Analysts surveyed by FactSet had forecast, on average, earnings of $1.03 per share on $25.64 billion in revenue.

The insurer repeated a 2012 forecast that calls for earnings to range between $4.55 to $4.75 per share on revenue of between $107 billion and $108 billion. Analysts have labeled that forecast conservative. They expect, on average, earnings of $4.77 per share.

UnitedHealth is the largest health insurer based on revenue and the first to report earnings every quarter. Many see the company as a bellwether for managed-care companies.

The insurer said its enrollment climbed 5 percent compared to the 2010 quarter to 34.6 million people, helped in part by Medicare Advantage growth. Those are privately run versions of the government's Medicare program for the elderly and disabled people. UnitedHealth is the largest provider of Medicare Advantage plans, and enrollment in that insurance is expected to grow as the baby boomer generation ages and becomes eligible for the plans.

UnitedHealth's medical costs also climbed 8 percent to $18.6 billion compared with the final quarter of 2010, when the insurer said it saw unusually low growth in health care use.

Insurers have been helped in recent quarters by health care use that has risen at rates that were slower than expected when they set premiums. Analyst see signs that this trend is continuing, but UnitedHealth CEO Stephen Hemsley warned last fall he expected use to return to more normal levels.

For the full year, UnitedHealth earned $5.14 billion, or $4.73 per share, on $101.9 billion in revenue.