INDIANAPOLIS (AP) — Health insurers Anthem and MDwise say they’re withdrawing from the Affordable Care Act’s insurance exchange in Indiana next year.

Both Indianapolis-based companies said Wednesday their decisions were based on fewer people than expected signing up for coverage and uncertainty over federal subsidies for the exchanges. The decisions affect about 46,000 Anthem and 31,000 MDwise customers.

Four Indiana counties — Grant, Posey, Warrick and Wayne— could have no exchange options next year without Anthem and MDwise, according to data compiled by The Associated Press and the consulting firm Avalere. About 4,600 people bought exchange coverage in those counties this year, with some 175,000 statewide.

The exchanges are the only way customers can get income-based tax credits to help pay premiums.

Insurer Centene Corp. plans to expand its presence on Indiana’s exchange.

Enough insurers are planning to sell coverage on the Affordable Care Act’s insurance exchanges next year to keep those markets working in most parts of the country.

Competition has dwindled, however, and another round of steep price hikes is expected to squeeze consumers who don’t receive big income-based tax credits to help pay their bill.

Health insurers had until Wednesday to declare whether they planned to sell coverage next year on the exchanges in most states. Actual participation and final rates won’t be set until later in the year.

The consulting firm Avalere expects more than 40 percent of U.S. counties to have only one insurer selling coverage on the exchange in 2018. Early plans filed by many insurers include premium increases of well over 20 percent.