There is so much uncertainty about Obamacare that Aetna, the U.S.'s third-largest insurance provider, may be forced to double its rates or opt out of the program, the company's CEO, Mark Bertolini, told CNBC on Thursday.

What action Aetna will take is still up in the air, but the company doesn't plan to set its 2015 Obamacare rates until May 15. Between now and then, though, Bertolini said he's trying to get the necessary information from the Obama administration to properly price its insurance products.



(Read more: CNBC Explains Obamacare)

"I think in the end analysis, pulling out is always the last resort," Bertolini told "Closing Bell."

"We don't like to do that because we disenfranchise customers and we disappoint customers, so we always look at that as a last resort, but that is an option that we will pursue if we need to if the program doesn't settle down; if we can't get a good handle on the data and the less data we have, the more risk premium we need to put into our products and that means the prices are higher."



To Bertolini, it's still unclear whether Aetna will need to expand its network or if people will be able to keep their program for another year, for example, under the Affordable Care Act.



Still, Bertolini said Aetna probably wouldn't withdraw from Obamacare completely. He said the insurer would decide to pull out of the program only on a market-by-market basis, based off of the level of competition and whether it can achieve an adequate return on capital.



Bertolini first threatened to pull out of Obamacare two weeks ago, in a "Squawk Box " interview from the World Economic Forum in Davos, Switzerland. Since then, he said the Obama administration has reached out to get the insurer the information it requires. Enrollment has grown, too, with 40,000 more paid members, he said.

(Read more: Aetna could be forced out of Obamacare: CEO)

Regardless of the grief it may have caused, Bertolini downplayed criticism of the many changes to the law since it was passed.



"If you take a look at a bill like Medicare, every year it gets tweaked or changed. So to expect that Obamacare hasn't been changed already and that the Affordable Care Act won't change in the future is probably not realistic," he said.

—By CNBC's Drew Sandholm. Follow him on Twitter @DrewSandholm.