Nathan Bomey

USA TODAY

Health insurer Aetna plans to cease its participation in the Obamacare health exchanges in all but four states.

The company's decision, which it blamed on heavy losses tied to the insurance plans, follows similar moves by competitors such as UnitedHealth Group, the nation's largest insurer.

Aetna said that in 2017 it would cease offering health care insurance options through the Affordable Care Act exchanges in 68.9% of the counties where it offered plans in 2016. It will continue offering certain plans in Delaware, Iowa, Nebraska and Virginia. Affected enrollees will keep their plans through the end of 2016 but must find alternatives for next year.

Aetna sustained a second-quarter pre-tax loss of $200 million on its individual health care plans, though that figure includes results from insurance offered outside of the Obamacare exchanges.

"As a strong supporter of public exchanges as a means to meet the needs of the uninsured, we regret having to make this decision," Aetna CEO Mark Bertolini said in a statement. "We will continue to evaluate our participation in individual public exchanges while gaining additional insight from the counties where we will maintain our presence, and may expand our footprint in the future should there be meaningful exchange-related policy improvements."

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Like other insurers, the company blamed its withdrawal on a pool of exchange participants that has turned out to be heavier users of their insurance plans than previously predicted. Insurers need healthy plan members to off set sick patients to balance the books.

Kevin Counihan, CEO of the government's Marketplace exchanges, said Obamacare is developing an "improving risk pool."

"Aetna’s decision to alter its Marketplace participation does not change the fundamental fact that the Health Insurance Marketplace will continue to bring quality coverage to millions of Americans next year and every year after that," he said in a statement. "It’s no surprise that companies are adapting at different rates to a market where they compete for business on cost and quality rather than by denying coverage to people with preexisting conditions."

The move also comes amid a fight between Aetna and the U.S. Justice Department over the government's lawsuit attempting to block the company's acquisition of insurer Humana. The government has said the deal violates anti-trust laws, but Aetna has said it will lower costs and improve choice.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.