What made mine worse was that, because he said it wouldn't hurt that bad, I agreed to allow the students to sit in on it. I was holding back tears the whole time and as soon as I got in my car I started bawling.

Basically they put a ton of saline in your uterus and then, like CSC said, they insert a probe into your vagina and they can see malformations or whatever by how the waves bounce in the saline. Another nurse called it a sonohysterogram. It's the same thing though.