Ohio, Missouri and Washington contain counties that as of now are not expected to have any Obamacare insurers selling plans next year .

Centene's announcement, which boasted of "another year of ... successful operations" on Obamacare markets by the company, bucks a trend of stories about insurers saying they will exit Obamacare markets , including several states that Centene is committing to.

Big insurer Centene has announced plans to enter the Obamacare markets of Kansas, Missouri and Nevada in 2018 , and also intends to expand its existing individual health plan business in six other states: Florida, Georgia, Indiana, Ohio, Texas and Washington.

Where President Donald Trump sees a "death spiral" for Obamacare , some insurers don't seem quite so pessimistic.

Obamacare supporters got some other good news in recent days when Aetna, which last month said it would not sell individual health plans in any of the four remaining states where it now does such business, filed proposed rates in Nevada for next year.

Aetna has said it has not made a final decision on whether to actually sell Obamacare plans in Nevada, but its filing increases its chances of winning a Medicaid plan contract with the state.

In Florida, the state's biggest insurer, Florida Blue, said it will sell Obamacare plans throughout the state next year.

UnitedHealthcare, the nation's largest insurer, filed tentative plans to do Obamacare business in New York and Nevada.

And Health Care Service Corp., which sells Blue Cross and Blue Shield plans, likewise has not made final decisions for next year but has filed tentative plans and rates for Illinois, Texas, Montana, Oklahoma and New Mexico.

Insurers nationwide have been unsettled by the Trump administration's push to repeal and replace key parts of Obamacare, particularly the provision that requires most Americans to have some form of health coverage or pay a fine. Another thing worrying insurers is the refusal of the administration and the Republican-controlled Congress to guarantee billions of dollars in federal payments to insurers to compensate them for plans that offer low-income customers reduced charges for out-of-pocket health costs.

Centene CEO Michael Neidorff, in announcing the insurer's expansion of Obamacare business in 2018, said, "Centene recognizes there is uncertainty of new healthcare legislation, but we are well positioned to continue providing accessible, high quality and culturally-sensitive healthcare services to our members."

"Centene has demonstrated disciplined execution, agility and capacity to successfully navigate industry changes to the benefit of our members, customers and shareholders."

Centene noted that the company grew from 537,200 Obamacare exchange customers at the end of 2016 to 1.2 million customers by March.

Watch: Centene CEO says he doesn't want to see 20 million people lose coverage