Routine prenatal ultrasounds billed as hospital services?

My insurance plan says it covers 100% of routine prenatal care, including ultrasounds, without copays. However, I have been getting bills for each ultrasound that have copays of various amounts, including a higher amount than what my specialist appointment copay is set for.

I called the insurance company and they said this is because the OBGYN is billing my imaging/ultrasounds as hospital services. This was surprising to me, because all my appointments and ultrasounds have been in the office setting. The insurance company told they only cover prenatal care at 100% when it’s performed in the office setting, and suggested I have the OB resubmit the claims saying they were performed in the office setting.

I then called my OB office, but they said it’s their policy to submit all imaging as a hospital service regardless of where it’s performed. They are part of a large nonprofit health system with a hospital, so I’m guessing they get better reimbursements from insurance companies by doing it that way. They said they could submit the claims for review, but it doesn’t sound promising that they’ll change anything.

Is this legal? Do I have any recourse? Under other circumstances I would just suck it up and pay the copays (right now it’s less than $200 so not unaffordable), but I’ve already spent thousands on healthcare this year due to other medical issues and with a new baby on the way, I really don’t want to pay a nickel more than I need to, especially when I shouldn’t have to.