If you're poor, uninsured and fall seriously ill, in most states if you qualify for Medicaid — but weren't enrolled at the time — the program will pay your medical bills going back three months. It protects hospitals, too, from having to absorb the costs of caring for these patients.

But a growing number of states are rescinding this benefit, known as "retroactive eligibility." On Nov. 1, Iowa joined three states that have eliminated retroactive coverage for some groups of Medicaid patients since the Affordable Care Act passed. Each state had to secure approval by the federal government.

Retroactive eligibility has been a feature of Medicaid for decades, reflecting the program's emphasis on providing a safety net for poor, disabled and other vulnerable people. In contrast to private insurance, determining Medicaid eligibility can be complex and the application process daunting, advocates say. A patient's medical condition also may keep families from applying promptly for coverage.

All four states -- Arkansas, Indiana and New Hampshire, in addition to Iowa -- have expanded Medicaid under the health law, which allowed states to include adults with incomes up to 138% of the federal poverty level, or about $16,000 for one person. So, in theory, most adults are required to have insurance under the ACA. In practice, each state still has a significant number of uninsured, ranging from 5% to 8% of the population.

The retroactive coverage "can compensate for the sorts of errors and lapses that can so easily occur on the part of both the applicant and the government bureaucracy" that delay applications, said Gordon Bonnyman, staff attorney at the Tennessee Justice Center, a public interest law firm that represents low-income and uninsured residents.

State and federal officials say eliminating the retroactive coverage helps encourage people to sign up for and maintain coverage when they're healthy rather than waiting until they're sick to enroll. It also fits into federal officials' efforts to make Medicaid, the federal-state program that provides health care for low-income adults and children, more like private insurance.

But consumer advocates and health care providers say the shift will saddle patients with hefty medical bills and leave hospitals to absorb more uncompensated care when patients can't pay. Some worry this could be the start of a trend.

In Iowa, the change applies to just about anyone coming into Medicaid — except for pregnant women and children under age 1. The change will affect up to 40,000 residents annually and save the program more than $36 million a year.

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"We're making it a lot more likely that Medicaid-eligible members are going to incur significant medical debt," said Mary Nelle Trefz, health policy associate at the Child & Family Policy Center in Des Moines, whose organization opposed the change.

When someone has a traumatic health event, the initial focus is to get them stabilized, not figure out how to pay for it, said MaryBeth Musumeci, associate director of the Program on Medicaid and the Uninsured at the Kaiser Family Foundation. (Kaiser Health News is an editorially independent program of the foundation.)

Patients may neglect to apply immediately for Medicaid, leaving them financially responsible for days or months of care they received before they got in their application, even though they may have been eligible for Medicaid all along.

That's not the only issue, advocates say. Unlike the commercial insurance market where re-enrollment through someone's employer is routine, Medicaid requires that beneficiaries' eligibility be reassesed every year.

"People fall through the cracks," said Andrea Callow, associate director of Medicaid initiatives at Families USA, a consumer advocacy group.

In addition, complications can arise for people who might need Medicaid coverage for long-term care services.

"The criteria are complicated. For a layperson to find those criteria and figure out if they're eligible" is challenging and they may need extra time, said Musumeci. Once patients have secured coverage, they may already have accrued hefty expenses.

Maybe so, but some people argue that a 90-day retroactive eligibility guarantee is counterproductive.

"We're trying to get people to behave more responsibly, not less responsibly," said Gail Wilensky, an economist who oversaw the Medicaid and Medicare programs in the early 1990s under President George H.W. Bush. "That is not the signal you're sending" with three months of retroactive eligibility. A 30-day time frame is more reasonable, Wilensky said.

In contrast to Iowa, the waivers in Arkansas, Indiana and New Hampshire generally apply only to adults who gained coverage under the law's Medicaid expansion. (Indiana's waiver also applies to other groups.)

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Kentucky has a request pending that, like Iowa, would eliminate retroactive Medicaid eligibility except for pregnant women and children under 1, according to KFF.

Under federal law, officials can waive some Medicaid coverage rules to give states flexibility to experiment with different approaches to providing services. And retroactive eligibility waivers in Medicaid are hardly new. A few states like Tennessee have had them in place for years. Tennessee officials eliminated retroactive eligibility for all Medicaid beneficiaries in 1994 when the state significantly expanded coverage under TennCare, as Medicaid is known there. At the time, the state even allowed uninsured people to buy into the program who wouldn't otherwise qualify based on income, said Bonnyman.

"There was no reason for anybody to be uninsured except undocumented immigrants," said Bonnyman. "It didn't seem to have the potential for harm."

But state officials revamped that program after serious financial problems. Eligibility for TennCare has become more restrictive again.

Other states that waived retroactive coverage for at least some Medicaid groups include Delaware, Maryland, Massachusetts and Utah, according to the Kaiser Family Foundation.

Bonnyman said his group frequently works with Medicaid beneficiaries who have medical bills they can't afford that accumulated during the months before they applied for Medicaid.

"If you're a moderate- to low-income working family, one or two days in the hospital is enough to ruin you financially," he said.

Kaiser Health News, a nonprofit health newsroom whose stories appear in news outlets nationwide, is an editorially independent part of the Kaiser Family Foundation.