Not sure. I've only been in there for follicle ultrasounds. Sometimes the techs take 15 minutes and I get close to snoozing off. I usually just stare at the ceiling and zone out. This time will be different though and I'm probably going to be in panic mode!
I think the reasons for the us matter... With follicle checks its a matter of medical opinion if they're ready ( I think ) and the techs can't make that decision.... With baby us they are a lot more free to point stuff out (a leg is a leg is a leg... ) they won't necessarily give you their opinion on things like uncalled fold testing (one of the markers for downs) or abnormal stuff, if that makes sense.
With my m/c, I could see the sac and see that there was nothing in it. I asked if what I saw was right and the tech (usually very talkative) was quiet and said "well, lets let the doc look at it" (or something along those lines).