WellPoint Inc. has lost nearly 850,000 members from its commercial health plans this year, and come 2014, a large chunk of its lucrative small-employer clients are likely to seek health coverage through new insurance exchanges.

That declining trend—headed toward a big cloud of uncertainty—has weighed on WellPoint’s shares, which suffered along with its peers in the post-election sell-off of health insurers. WellPoint shares finished last week at $56.16 apiece, down 8 percent from Election Day on Nov. 6.

The declines persisted even after Well Point reported better-than-expected profits from the third quarter.

Indianapolis-based WellPoint derives the lion’s share of its profit from small employers who buy full insurance—as opposed to simply hiring WellPoint to process claims and run wellness programs.

But the average WellPoint small-employer client has just 8.5 lives covered on its health plan. And firms of that size are far more likely to use the new health insurance exchanges, WellPoint Chief Financial Officer Wayne DeVeydt said during a Nov. 7 conference call. Small-group employers are defined as having 50 workers or less.

"The smaller the size of employer group, the more that we anticipate that it will migrate to an exchange," DeVeydt said. "And while we've built a number of strategies to keep those employers within our current book of business ... we want to be prepared for the fact that the vast majority of our small-group business is smaller scale in size."

WellPoint could still hold on to those clients by selling them coverage through the exchanges. But the 2014 shift is like putting a huge portion of WellPoint’s business up for bid all at once. And investors have not reacted favorably to the uncertainty of that scenario.

WellPoint officials say the trusted brand name of their Blue Cross and Blue Shield plans will have a powerful appeal in the exchanges, which will most likely operate like online marketplaces where consumers can compare plan features and price.

The exchanges also will offer subsidies to consumers with incomes less than 400 percent of the poverty limit, which is expected to add 16 million customers to the commercial insurance business nationwide.

“For the exchanges it's actually a change but an opportunity, and there will be a lot more people covered,” said Ken Goulet, president of WellPoint’s commercial business unit. “And we feel that with our brand and with our product positioning, we're going to be in good shape to be able to participate on the exchanges”

But Goulet also acknowledged that the losses in WellPoint’s commercial business will continue in 2013, although not as sharply as they have this year. The gains, he said, won’t come until 2014.

“We're believing that there will be normal trends going into the first half of the [next] year. But in the second half of the year there will continue to be some turnover,” Goulet said during the conference call. “But new sales will wait until the exchanges become available in 2014. So our individual segment marks down a little bit in the second half of 2013, but will pop back up once we head into 2014.”