ATLANTA The cancer had already spread to her abdomen by the time Beth Brock managed to escape from her health insurance nightmare.

The Woodstock business owner learned last fall her insurance didn't meet the Affordable Care Act's new standards, so she reluctantly chose a different health plan that her doctors assured her they accepted. But they didn't.

Brock, 48, was waiting at her OB/GYN for a pre-surgical visit the last step before an operation to remove an ovarian cyst when the billing office called to say it didn't accept her new plan after all. It would be two months before she untangled the mess and switched to a health plan that covered a broader array of doctors. By then, the cyst had grown from slightly larger than a walnut to bigger than a softball.

"I had lost all that time," said Brock, who is undergoing chemotherapy. "If (the surgeon) could have operated on me in January ... it wouldn't have had the opportunity to grow huge and spread."

Her chance of living for another five years is 40 percent.

Nearly nine months after the scrambled launch of the federal Health Insurance Marketplace, some Georgians have been shocked and dismayed to find their new insurance plans offer far fewer doctors, specialists and hospitals to choose from than they've come to expect.

The so-called narrow networks, experts say, enable insurers to curb costs and, in turn, offer lower premiums to consumers. Nationwide, nearly half of all federal marketplace networks are considered narrow.

The trend is not limited to Obamacare plans. The Affordable Care Act may have hastened the trend, but employers and insurers in recent years have increasingly turned to narrow networks to rein in health care spending. That means millions of Americans not just those with marketplace plans may be choosing from smaller lists of doctors and hospitals in years to come. Brock, for example, did not buy a marketplace plan but still wound up with a limited network.

As part of the health care overhaul, insurance companies may no longer deny coverage to Americans with high-blood pressure, heart disease, diabetes or other pre-existing conditions. They also can't charge exponentially higher premiums to people because they are women or sick or getting older.

The changes have made affordable health coverage a reality for millions of previously uninsured Americans. But the greater regulation has also left narrow networks as one of the last major tools insurers can use to lower costs and keep their premiums competitive.

"In the past, they didn't compete on networks, but they didn't take anyone who was sick," said Gary Claxton, vice president with the nonprofit Kaiser Family Foundation. Now, "networks are what they got."

Anne Isenhower thought she did everything right.

Before buying a plan on the Health Insurance Marketplace, the Dunwoody communications consultant and mother called Piedmont Healthcare and her insurer to make sure regular visits to her doctors would be covered. They said, "We can just switch you over, no big deal," she recalled. But Piedmont denied the insurance when Isenhower, 47, showed up months later to prepare for a corneal transplant.

Last fall, widespread confusion amid the marketplace's rollout left patients and doctors in some cases befuddled by the new narrow networks. Some providers didn't know whether they were included in the networks until months after the coverage took effect.

Like many other marketplace plans, Isenhower's 'Pathway X' plan through Blue Cross and Blue Shield of Georgia doesn't include three of metro Atlanta's most prominent health care systems Piedmont, WellStar Health System and Emory Healthcare.

"The 'X' on your card is like a scarlet letter," Isenhower said.

Blue Cross is hardly the only insurer with narrow networks. Humana, for example, also offers an HMO marketplace plan with a narrow network that limits adult Atlantans to using Northside Hospital and its affiliates, plus Atlanta Medical Center downtown.

Indeed, half of federal marketplace plans feature the scaled-back networks, according to an analysis by global consulting firm McKinsey & Company. The Georgia Department of Insurance has received about 30 complaints from consumers about marketplace networks being too narrow, a spokesman said. Nearly 230,000 Georgians have enrolled in marketplace plans, the latest state data shows.

It works this way. Some insurers narrow networks by excluding the most expensive hospitals or doctors. Others make a deal with a provider in which the insurer pays lower reimbursement rates but sends a greater volume of patients to those doctors or hospitals. In yet another approach, insurers charge higher co-pays for certain providers, effectively creating a narrow network.