Ultrasound involves a lot more than a photograph does. It's neither been proven dangerous nor safe. I'm not telling you what to do, Mandamom, but you should make a fully informed decision about unnecessary/medically uncalled for ultrasound, esp the more intense 3D type. I do understand how fun they can be. Not knowing the possible risks, I had ultrasounds at least once a month with my first son. I was pregnant in Korea where we could have one done for less than $10 a pop.
Anyway, here is some info that you might want to read.
http://www.midwiferytoday.com/articles/ultrasoundrodgers.asp
http://www.unhinderedliving.com/pultra.html
Follow Mothering