Health insurer Cigna Corp. said on Thursday it would not expand its participation in the government-run health exchanges next year, joining an industry pullback from the struggling business.

Cigna, which manages insurance plans for big companies and sells health plans on the exchanges created under the Affordable Care Act, had planned to expand into 10 states from seven.

Insurers including Aetna Inc., UnitedHealth Group Inc. and Anthem Inc. — which has agreed to buy Cigna — say they are losing money on the exchanges because of lower-than-anticipated enrollments. Enrollees are also sicker and older than expected, the companies say.

UnitedHealth and Aetna announced earlier this year that they would leave the exchanges in 2017.

The U.S. government has moved to block the Cigna-Anthem deal, saying it would stifle competition.

Shares of Cigna, which reported a better-than-expected third-quarter profit, fell 54 cents to close at $117.31 on Thursday.