E.W.
I too found out the sex of my daughter in the first ultrasound, but I was very leery and didn't want to start buying anything yet just in case they were wrong. When they told me in my second ultrasound that is when I finally believed them. I also did a 4D Ultrasound about half way through the pregnancy and it was wonderful! There they said to drink a juice before the ultrasound because the sugar gets the baby moving around, and it worked.