Hello ladies!

i have my first ever ultrasound on friday. It will be my 12-13 week one. I am having the D/S scan done as well.
What should i expect. Am i supposed to drink heaps of water before hand?
Do you have to wear anything in particular or do they give you a gown?
Also i have read in a couple books that the babies genitalia is formed bu now??? Is it possible to tell the sex at this stage?

I have no idea what to expect! any help would be great!!!

Thanks!!

Ambz