I did this once when I was a teen. It was so miserable!! I had to pee so badly in the waiting room! My mom kept saying "You're fine! Just hold it!" and I was almost in tears!

They did part of the ultrasound and told me to go to the bathroom but not to let it all out. Well when you have to pee THAT badly, you can't start peeing and then stop. It all comes out! lol