UnitedHealth, the nation's biggest health insurer, will remain in public health insurance exchanges in only a handful of states next year after expanding to 34 this year.

UnitedHealth, the nation's biggest health insurer, will remain in public health insurance exchanges in only a handful of states next year after expanding to 34 this year.

CEO Stephen Hemsley told analysts Tuesday morning that the company cannot continue to broadly serve the market created by the Affordable Care Act's coverage expansion due in part to the higher risk that comes with its customers.

The state-based exchanges are a key element behind the Affordable Care Act's push to expand insurance coverage. But insurers have struggled with higher than expected claims from that business.

UnitedHealth Group Inc. has estimated that it could lose as much as $475 million on its public exchange business this year. It has already decided to pull out of Arkansas, Georgia and Michigan in 2017.