The cost of giving birth in America has skyrocketed in recent years — even for women with employer health insurance.

A major study looking at women with employer-provided health insurance found that the average new mom spent $4,500 out-of-pocket to give birth in 2015, the most recent year data are available. That's a 50% increase from 2007, when the typical new mom paid out just over $3,000 of her own money. It's also more than three times the rate of inflation over that time period.

"I don't know a lot of patients who have this kind of funding lying around," said Michelle Moniz, an assistant professor in obstetrics and gynecology at the University of Michigan and the study's lead author.

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Moniz, a practicing physician, added: "These expenses are coming at a time when most of my patients are thinking of everything else on their baby list — a crib, a car seat, everything they need to keep their newborn safe — and they aren't expecting a bill like this."

The cost of one birth — in itself the most common reason for a woman to be hospitalized in her lifetime — is now more than the typical woman earns in a month. The average full-time worker in America makes just over $41,000 a year, or around $3,400 a month, according to the U.S. Labor Department.

And the more than 650,000 women in the study, which was published this week in the academic journal Health Affairs in many ways represent a best-case scenario: They are in large employer-sponsored health insurance plans, which are typically more generous than plans offered by small businesses or purchased individually. These plans cover about half of U.S. births.

Moniz and her coauthors found that the actual cost billed for the birth stayed mostly steady over the seven years in the study period. What changed was the growing portion paid by patients: The typical deductible payment rose from just over $1,500 to nearly $2,500, while the typical coinsurance (a portion the insured patient pays after meeting their deductible) rose about $300.

"I was completely surprised that the phenomenon of having to pay something out of pocket for maternity care was almost universal," said Moniz. "98% of people had some out-of-pocket cost by the end of the study."

The study takes aim at a common misconception that the Affordable Care Act, which mandated coverage for maternity benefits, made it cheaper to have a baby.

"For people who talk about the ACA, there seems to be this misconception that 'Oh, maternity's covered,'" Moniz said. In fact, while large employers are required to provide maternity-care coverage, that coverage can include significant payments from the patients. That concerns Moniz, especially as the maternal mortality rate is increasing in the U.S.

"Our hope is that policymakers take note now and change the situation," she said. "We want every family to get off to the best start in life, and this is an irremediable barrier."