What's the difference?

Well, one of the signs is when it happens when you stand up after laying down for a while. You'll have to go in to L&D and have a lab test done. That's how I knew with my first, no other signs of labor. They were ready to send me home, the nurse was so sure it was pee, but I had had absolutely no incontinence the entire pregnancy. Lab test showed it was amniotic fluid and I was admitted.

Audrey is right, they can test the fluid to see what it is to get a for sure answer.

But, to check at home before going in, I've heard if you're unsure, you should empty your bladder, put a pad/pantyliner on, and go lay down for 30 minutes or so. Then, stand up while flexing your urinary sphincter (like you're trying to hold your pee). Then, if you leak anything, it should be caught in the pad.

Your doctor will likely want to know color, amount/frequency, smell, and if you're able to hold it in.

Color - amniotic fluid is usually clear or pale yellow
Smell - amniotic fluid is usually odorless or kind of sweet smelling
Ability to hold it - there's no sphincter to control amniotic fluid, so you shouldn't be able to hold it in

If those all point to amniotic fluid, they'll likely want you to come in to get that lab test done.

Amount & frequency - This will tell them if they need to worry about infection risk and too much fluid loss