CHICAGO -- At Rush University Medical Center on Chicago's West Side, the median charge for a vaginal birth was $16,703 last year.

Three miles away, at Norwegian American Hospital, it cost about half that: $8,873.

Most patients don't pay those charges, instead paying a sum based on rates negotiated between hospitals and health insurance companies. But even after those negotiations, stark differences often remain -- disparities that can hit the wallet hard.

Though consumers have long bemoaned rising health care costs, few people shop for health care the way they might shop for a car, comparing prices. Some don't realize a procedure can cost tens of thousands of dollars more at one hospital versus another. Others would rather rely on referrals or don't know where to go to find information. Hospital prices vary for a number of reasons, including differing overhead costs, market dynamics and, in some hospitals, a need to offset the costs of complex services by billing higher rates for simpler ones.

Now, the Trump administration wants to make it easier for patients to comparison shop for medical care, proposing a rule that would require hospitals to post their charges, before insurance, on their websites. The administration also is considering whether that posted information should reflect rates negotiated with insurers.

Some consumer advocates cheer the administration's proposal as a step toward greater price transparency. But hospitals and many experts say such a move likely wouldn't make much of a difference, pointing to existing online price comparison tools that often go unused by consumers. They also question the usefulness of posting charges before insurance.

"Everybody wants to try to find a path forward to increase price transparency, but it is very complex," said Sandy Kraiss, Illinois Health and Hospital Association vice president of health policy and finance. "We just don't see that this is the best approach to advance that."

Consumers who want to know how much a hospital procedure will cost already have a number of options.

They can call hospitals to get individual estimates, and sometimes, they can go to hospital websites. Late last year, west surburban hospital system Edward-Elmhurst Health became one of the few systems to post a pricing tool on its website to help consumers estimate out-of-pocket costs based on their insurance plans.

The Illinois Department of Public Health also lists median charges, by hospital, online in its hospital report card, but those figures show only list prices, not how much a patient will actually pay after insurance.

Insurers offer many of the most comprehensive price-comparison tools. In many cases, consumers can log onto their insurance companies' websites to compare their individual, out-of-pocket costs for procedures at different hospitals.

Illinois' largest insurer, Blue Cross and Blue Shield of Illinois, has had an online tool in place for about eight years for members to compare prices and quality -- partly as measured by outside organizations -- across hospitals. Yet less than 10 percent of members use the tool, said Thomas Meier, the insurer's vice president of market solutions.

It's not an uncommon result. Nationally, only about 20 percent of Americans have tried to compare prices before getting care, according to the results of a 2016 survey by Public Agenda, a New York City-based nonprofit.

Experts chalk up the low numbers to several factors, including a lack of consumer knowledge, interest and time.

"A lot of it is member awareness," said Meier with Blue Cross and Blue Shield of Illinois. "I think a lot of the members don't understand even what an (in-network) versus out-of-network provider is, let alone that 44 different providers would charge 44 different amounts for an MRI."

Also, for many consumers seeking health care, price isn't top of mind, said Sunita Desai, an assistant professor in health policy at New York University. She was lead author of a study published in the journal Health Affairs last year that found only about 12 percent of a large population of employees who were offered a price transparency tool used it.

Patients in the throes of a medical emergency don't have time to price shop. Those who do have time may trust only certain doctors. And in some cases, price shopping might not help a patient save money, Desai said. Finding a lower-cost service helps a patient only if that service costs less than his or her insurance deductible or out-of-pocket maximum.

"People aren't necessarily using them because, in some cases, they don't really have any incentive to do so," said Sally Rodriguez, chief of staff at the Washington, D.C.-based Health Care Cost Institute, of cost transparency tools.