what happens at your 1st fitting?

Dumb question perhaps, but I don't know!

Have they done any work to the dress at this point or do they try it on you and begin the alterations?

I want to change the top a little and don't know if I need to tell them now or wait until my first fitting. I just ordered my gown this past weekend so I have plenty of time.

What happened at your first fittings?

If you want to change the top and it's something that can be done in the production process, then I assume you'd check with the shop so they can see if the designer will make the changes to the dress.
Otherwise, it's up to the seamstrss, in which case you'd tell her at your first fitting.
Basically the first fitting is when you try on the dress with all your undergarments and your shoes, the hem is done, you can decide on bustles, it's taken in or let out and basically nipped and tucked in all the right places.
2nd fitting it to try it on after the alterations are done and to do any more if necessary and by the 3rd it should be perfect.