NEW YORK (Reuters) - Insurer Cigna Corp yesterday reported a lower-than-expected quarterly profit on weakness in its main health care segment.

The company affirmed its full-year earnings-per-share forecast, but slightly lowered its projection for health care profit. It also cut the top end of its targeted range for health care membership growth.

Although Cigna's shares were down 20 percent this year at yesterday's close, the stock had outperformed rival US health insurers, which have largely posted disappointing results this quarter and cut their 2008 outlooks.

"In somewhat of a recurring theme in Cigna's reports, other non-core businesses offset weakness in core health care results," JPMorgan analyst William Georges wrote in a research note.

Cigna shares fell four percent to $41 in light trading before the market opened.

Net income slumped to $58 million, or 21 cents per share, from $289 million, or 98 cents per share, a year earlier. The latest results include charges for litigation and a change in accounting for the company's reinsurance business.

Excluding items, earnings were 94 cents per share, two cents below the analysts' average forecast, according to Reuters Estimates.

Revenue rose 4.5 percent to $4.57 billion.

Health care earnings fell nearly 18 percent to $138 million, hurt by weaker margins and lower-than-expected membership.