yes they will measure baby and look to see if they can see major internal organs and what not, generally just making sure all looks ok and in order, all limbs present and correct, that sort of thing. it's horrid being nervous before scans. with my first pregnancy i was always convinced there would be no baby in there and the hospital staff would all laugh at me! have a cup of tea (or six, full bladder and all that) and try and look forward to seeing the baby on the screen i hope it goes well for you
measure the head, the tummy and the femur (thigh bone), view the bladder, the kidneys, the stomach, the lips, the whole of the spine, upper limbs, hands, feet, four changes of the heart, the brain, the placenta, the umbilical cord and measure the liquor.
I had mine yesterday and was there for nearly two hours! They were trying to see all four chambers of the heart, took ages as bubba was in an odd position!!
I don't have that big a bump and was petrified and everything was fine.
Oh and I was supposed to have a full bladder, but I didn't as I forgot, this wasn't mentioned!