Hi Maria,
Usually if you're around three months' pregnant, they try and get the picture of the baby by running the scanner over your stomach. If they can't get a clear image this way, then they try a trans-vaginal scan using a probe. If you are much earlier on in your pregnancy, they may just try the vaginal route.
When I went for my first dating scan (in my first pregnancy), I was 13 weeks' pregnant, but because I had a tilted uterus - which is quite common - they couldn't see the baby, so had to do the transvaginal scan. It couldn't have been too bad because I have no bad memories of it! In fact, I can't really remember it at all: I was too excited about seeing the baby.
To help the sonographer do an abdominal scan, they usually tell you its best to have a full bladder. I've also read that it's best not to have a lot of gas in your bowel, perhaps because the "swooshing noises" in your intestine can interfere with the sound waves in your uterus that they're trying to pick up. This means that you should try to avoid high fibre foods the day before.
I hope it goes well and that you get to see your baby clearly in there - for the first time! - so exciting, eh?
What do they do?? is it a tummy scan or an internal scan, i have no idea lol
