PHILADELPHIA (Bloomberg) — Cigna Corp., the fourth-largest US health insurance provider, said earnings rose 15 percent as membership grew in medical plans employers buy for workers and their families. The shares jumped the most in three months after Cigna raised its forecast.Third-quarter net income climbed to $298 million, or $2.75 a share, from $259 million, or $2, a year earlier, the Philadelphia-based company said yesterday. The increase was the first in more than a year. Profit excluding investment gains and discontinued operations was $2.48 a share, beating analyst estimates.

Cigna’s customer enrolment increased 2.8 percent in the last 12 months to 9.3 million.

Chief executive officer Edward Hanway bought benefits company Star HRG in June, adding 200,000 people employed by more than 1,000 corporate clients. Star specialises in low-cost health plans with limited benefits, a type of insurance that Cigna and other health insurers hope will help expand sales for uninsured Americans.

“Membership is slightly better than expectations,” said William Georges, an analyst with JP Morgan Chase & Co. in New York, in a note to investors today. “Cigna delivered a solid third quarter.”

Enrollment in Cigna medical plans may rise 4 to 6 percent in 2007, Hanway said on a conference call today. Medical membership will rise one to two percent this year, in addition to enrolment gains from the Star purchase, Cigna said in its statement.

The proportion of every premium dollar Cigna spent on medical care rose to 85.7 percent from 84.4 percent a year earlier, excluding the Star purchase and adjustments to reserves. Medical costs will rise 6.5 to 7.5 percent next year, Cigna said.

Adjusted profit beat the average $2.17-a-share estimate of 17 analysts surveyed by Thomson Financial. Thomson didn’t disclose how the estimates were calculated. Revenue rose 2.9 percent to $4.1 billion.

Hanway projected 2007 profit from operations will rise to $9.50 to $10.10 a share from an increased forecast of $8.85 to $9.15 this year. Cigna said income from operations this year will be between $995 million and $1.035 billion, up from an August forecast of $960 million to $1.02 billion, or $8.30 to $8.80 a share.

“We are demonstrating the ability to take market share from our competitors and we see meaningful opportunities for growth,” Hanway said on yesterday’s call. Cigna will continue to focus sales efforts on employers that buy coverage for workers, he said.