In the filing with the U.S. Securities and Exchange Commission, Aetna raised its forecast of 2011 operating earnings to $5.15 per share. That's up from a $5-per-share estimate in late October, and it's better than the $5.02 per share prediction of analysts surveyed by FactSet.

The company said 2012 operating earnings should be about $5 per share — up from a forecast of at least $4.80 per share in October. Analysts expected $4.96 per share.

Aetna has been helped this year as weaker use of medical services in a sluggish economy has held down costs.

Hartford, Conn.-based Aetna also said again that it expects to lose a half-million members from its commercial administrative services contracts in the first quarter. Company officials have said that the weak economy has prompted some large corporate customers to pick health plans with fixed costs.

The company said that medical membership will grow slightly in the fourth quarter, then drop from a projected 18.4 million on Dec. 31 to 17.9 million by the end of March 2012. It forecast that membership will grow again over the last nine months of 2012, but it didn't provide a figure.

Aetna expects 35,000 more Medicare members in the first quarter, but 80,000 fewer in Medicaid as it leaves the Medicaid program in Connecticut.

Company executives are expected to discuss strategy and outlook during an investor conference Thursday in New York.

In Wednesday's filing, Aetna also said that through last week, it had spent $1.6 billion to buy back about 40 million shares this year.

Aetna shares fell 33 cents in regular trading to close at $39.28.