Insurance denied ultrasound?!

I got a packet in the mail saying that coverage for my next ultrasound had been denied. Has anyone else had this problem? I don't care about finding out what the sex is I just want to know of my baby is going to be okay since with my first ultrasound they told us that our baby had too much fluid behind its neck. I just don't know what I'm going to do if they don't let me see my baby or make me pay some ridiculous amount...