Health insurance plans that limit the number of hospitals and doctors that patients see make up the majority of Obamacare plans, and plans are expected to become even more restricted in 2018, according to an analysis published Thursday by the consulting firm Avalere Health.

The firm found that 73 percent of plans that will become active in 2018 have more restrictive networks, up from 68 percent in 2017 and 54 percent in 2015. Creating narrow networks of providers is one way that health insurance companies keep costs in check, both to their bottom lines and for their customers. For Obamacare customers, it can mean losing coverage for a particular doctor that they had been seeing for years, or in some cases only receiving coverage for medical providers that are further away than other options they would otherwise have in their area.

“We continue to see insurers focusing on narrow network exchange products that enable them to offer competitive premiums and manage medical costs,” Caroline Pearson, senior vice president at Avalere, said in a statement. “These narrow network plans may come at a lower price tag for consumers, but they may also limit consumer choice and access to specialist care.”

Avalere's analysis found that deductibles for silver plans, which are the mid-level plans most people bought in previous years, will rise to an average of $3,937 in 2018, or an increase of $234 since 2015. Deductibles are separate from premiums, and are the amount of money that patients owe on different procedures or medical visits before health insurance kicks in to cover the rest. The deductible starts at zero every year, so a patient can pay the full amount several years in a row depending on their medical needs.

Individuals who make less than 250 percent of the federal poverty level, or about $29,700 a year, are shielded from these increases because they receive cost-sharing reduction subsidies. Though President Trump ended the payments in October, insurers are still required by law under Obamacare to provide them, and many have done so by increasing the costs of premiums on other enrollees.

To assemble the report, Avalere analyzed plan information for states that use healthcare.gov, as well as for California and New York, which have their own exchanges.