I've written a decent amount lately about the challenge of shopping for medical treatment. My own experience centered on the difficulty of shopping for an MRI, but new moms Erin Taylor and Layla Parast share another insightful example of the difficulty shopping for another common medical experience: giving birth.

The two women are co-workers with the same insurance plan. By coincidence, they happened to become pregnant around the same time and gave birth at the same hospital. They both selected in-network obstetricians to deliver their babies. Both chose to receive an epidural from an anesthesiologist as they gave birth — and that's where things began to diverge. Here's more from their co-authored blog post at Health Affairs:

Layla received an unexpected bill for $1,600 for anesthesiology services and warned Erin to expect the same. Yet Erin’s bill never came. Layla happened to deliver on a day when an out-of-network anesthesiologist was on call, while Erin was seen by an in-network anesthesiologist. Purely by chance, one of us received an expensive physician bill and the other did not have to pay a dime.

The two later figure out what happened: While the hospital they chose was in-network for the health insurance plan, Layla's anesthesiologist was an out-of-network provider. Just because he worked at the hospital, that didn't guarantee that he was one of the doctors that the insurer had in contract.

"Who would have the presence of mind during labor to ask whether the anesthesiologist on call is part of her insurance network?" Taylor and Parast write in their blog post. "While providing patients with information regarding which physicians are in network is an important part of health insurance transparency, it is meaningless in situations where the patient has no choice."

Layla ultimately did get her insurance to reimburse her for part of the bill but was still left with a $560 charge — while Erin didn't face any fee at all.

This issue of out-of-network providers working at in-network hospitals isn't especially rare, and has come up in other reports. The New York Times wrote about a man who received a $117,000 bill from an out-of-network assistant surgeon who the man didn't even know had participated in his surgery.

These cases suggest one of the peculiarities of shopping for medical services: It is, perhaps, the only good one can purchase while completely unconscious — and is often consumed in moments of severe pain, as would be the case with the epidural. Shopping for cars will always be easier than shopping for health care, because we'll always have the advantage of having our senses about us.