I agree with the majority, that insurance will usually pay for one u/s at around 18-20 weeks, and then deny coverage for the rest unless they are medically necessary.
I had several u/s's at the beginning of each PG because I was high risk for ectopic pregnancy. Then I had the standard u/s at 18 weeks. With Hannah they repeated the u/s 2 weeks later because there was a question about her kidney development. It was fine and insurance covered it. I also had several towards the end because I was hospitalized at 31 weeks with premature rupture of membrane.
With Emily I had the several initial ones, the 18 week one, and one around 36 weeks. I was measuring larger than expected and the midwife wanted to take a look. The insurance company denied coverage at first, then after I called to complain, the hospital re-coded it so it was covered. It's all about medical necessity.
Here's an interesting story about coverage. I was brought into the hospital at 31 weeks with Hannah and monitored for the day. I was told I was on complete bed rest. Since I got there at 6AM and hadn't had time to eat, I asked for breakfast and they sent some up. I was billed $7 for this because I had not yet been officially admitted (I was later that evening). I fought with the hospital and insurance company for a long time about this one. What was the alternative? Let a pregnant lady starve, or have me run to Dunkin Donuts for a snack? I can't remember if the hospital wrote it off or the insurance company paid, but I didn't.
Good luck to the OP when you are ready!
Denae