WellPoint Inc. reported second-quarter profit that missed analyst estimates as higher medical costs and lower enrollment weighed on results. The company trimmed its full-year forecast.

Earnings excluding one-time items were $2.04 a share in the quarter, the Indianapolis-based company said in a statement Wednesday morning. The result was lower than the $2.08 average of 19 analyst estimates compiled by Bloomberg.

WellPoint shares dropped more than 12 percent, or $7.41, to close at $54.01 on Wednesday, their lowest price since September 2010.

Net income fell 8.3 percent to $643.6 million, or $1.94 a share, from $701.6 million, or $1.89, a year earlier.

Revenue increased to $15.4 billion from $15.1 billion.

Full-year profit is expected to be $7.30 to $7.40 a share, the company said.

The lowered forecast will hurt “a stock that investors already dislike,” Thomas A. Carroll, a Stifel Nicolaus & Co. analyst in Baltimore, said in an e-mail. “There was lots of talk of medical trends rising and higher utilization. That will have sector-wide implications.”

WellPoint, along with its competitors, benefitted from lower medical costs last year, as Americans stayed away from the doctor amid unemployment rates that topped 9 percent. Those costs have stabilized this year, making it harder to increase profit, said Ana Gupte, a Sanford C. Bernstein & Co. analyst in New York.

“Cost trends have been flattening out as opposed to declining,” Gupte said in an interview before the announcement. “Last year, the whole industry had a really favorable tailwind, whereas this year, it’s been a different story.”

CEO Angela Braly has tried to add business ahead of President Obama’s health-care law, which is also expected to squeeze profits. The company said July 9 it would pay $4.9 billion for Medicaid insurer Amerigroup Corp. In June, it agreed to pay about $900 million for eyewear retailer 1-800 Contacts.

The company released results before the market opened. On Tuesday, shares of WellPoint, the nation's second-biggest health insurer, fell less than 1 percent to close at $61.42. Through Tuesday, the stock was down 7.3 percent for the year.

Analysts had estimated full-year profit of $7.76 a share on average.

Membership in WellPoint medical plans fell 2.3 percent, to 33.5 million, driven down by what Chief Financial Officer Wayne DeVeydt called “the competitive nature of certain markets” in Wednesday’s statement. The declines came in the insurer’s commercial accounts, where WellPoint raised fees for some policies. That eclipsed gains among government-backed Medicare and Medicaid plans.

“We are disappointed with the need to lower our guidance, but believe it is the right action to take, given the challenging market we see,” Braly said.

The insurer on June 15 said full-year profit was forecast to be at least $7.57 a share. The company also said that day that it would pay $90 million this year to settle a lawsuit over its decision to become a publicly traded company in 2001. That charge, along with costs from the 1-800 Contacts deal, are being taken this year, the company said in statements last month. The Amerigroup purchase is set to close next year.

UnitedHealth Group Inc., the biggest U.S. health insurer, announced earnings last week that beat analyst estimates, as enrollment climbed in Medicare plans for the elderly and Medicaid plans for the poor. The Minnesota-based insurer also raised its full-year profit forecast for 2012.