INDIANAPOLIS (AP) — WellPoint Inc. cut its 2012 earnings forecast on Wednesday after net income fell more than 8 percent, the health insurer’s enrollment slipped and medical costs climbed during the second quarter.

The company’s shares sank more than 6 percent in premarket trading.

Chairwoman and CEO Angela Braly said in a statement the Indianapolis company was disappointed that it had to lower its forecast but believes it is the right move as it deals with the rising cost of medical care and other challenges.

The insurer now expects 2012 adjusted earnings, which exclude one-time items, to range between $7.30 and $7.40 per share, down from a previous forecast for $7.57 per share.

Analysts surveyed by FactSet expected, on average, earnings of $7.76 per share.

In the second quarter, WellPoint reported net income of $643.6 million, or $1.94 per share. That’s down from $701.6 million, or $1.89 per share, a year ago when the company had more shares outstanding.

Adjusted earnings were $2.04 per share.

Operating revenue, which excludes investment income and gains, climbed 2 percent to $15.17 billion.

The performance missed Wall Street expectations. Analysts had forecast, on average, earnings of $2.08 per share on $15.31 billion in revenue.

Its shares fell $4.10, or 6.7 percent, to $57.32 in premarket trading.

WellPoint is the second-largest health insurer based on enrollment, trailing only UnitedHealth Group Inc. It runs Blue Cross Blue Shield plans in 14 states, including California, New York and Ohio. Membership fell 2 percent in the second quarter to 33.5 million people compared to last year’s quarter.

The insurer’s benefit expense, or what it paid in medical claims, climbed 1.4 percent to $12.09 billion in the quarter.

Insurers have been helped in recent quarters by health care use that has grown at lower-than-expected rates. WellPoint said use picked up in the second quarter, but it pointed price increases as the main factor behind rising medical costs.