FILE PHOTO: The office building of health insurer Anthem in seen in Los Angeles, California February 5, 2015. REUTERS/Gus Ruelas

NEW YORK (Reuters) - U.S. health insurer Anthem Inc said on Friday that it will no longer offer Obamacare plans in 17 counties in Missouri but will remain in the bulk of the state, covering 68 counties that would not otherwise have Obamacare coverage for their residents.

Health insurers are facing an upheaval in their businesses amid growing uncertainty about healthcare legislation under President Donald Trump, who seeks to follow through on his promise to dismantle former President Barack Obama’s signature healthcare law, formally known as the Affordable Care Act.

Insurers such as UnitedHealth Group Inc, Aetna Inc and Humana Inc have exited most of the states where they sold Obamacare plans, leaving hundreds of U.S. counties at risk of losing access to private health coverage in 2018.

But other insurers, including Centene Corp, have filled those gaps, expanding into counties that had lost their coverage options.

Every U.S. county is currently projected to have at least one insurer offering Obamacare individual coverage next year. Still, 1,476 counties could have only one insurer in 2018.