Even getting the prices wasn't easy. Hsia's team had to tease it out from state data on each patient admission. They figured out which ones were for childbirth, and then eliminated any complicated cases.
"Of course we would expect that if woman is in the hospital for six days as opposed to for two days, she would have larger charges," Hsia said. "And if you deliver a baby in San Francisco, it will be more expensive than if you deliver in a cheaper suburban area."
But the prices her team found — they are not naming individual hospitals — varied way more than these differences should account for.
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The main problem is that patients do not know how much their insurers are paying on their behalf, and they certainly don't know the price up front, Hsia says.
"This study shows that the market doesn't take care of health care the way that we would like," Hsia said in a telephone interview.
"If I go to buy a dozen eggs at the grocery store, I know if they are cage-free," she added. "As a consumer, I know what I am buying and why there might be price differences. But as a patient, I don't even know what things cost."
Health experts say this is one of the main reason U.S. health care is so much more expensive than in other countries — $8,915 per person in 2012, for a total of $2.8 trillion. Of that, $882 billion is spent on hospitals services, like giving birth.
In May, the federal government said it would start publishing data on hospital charges. Their first numbers confirmed what health reform advocates complained about for years: The charges vary enormously, and for seemingly unclear reasons.
The Obama administration hopes that publishing prices will help force health care providers to be more consistent in their billing.
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Last year, a team of researchers at at the University of Iowa compared the prices of hip replacements at hospitals across the United States. Prices ranged from $11,100 to $125,798, they reported in the Journal of the American Medical Association publication JAMA Internal Medicine.