How can i tell if the frog in my fishtank is pregnant?

ive got 2 of those little frogs that go in your fish tank with the fish.. the female frog seems to be looking fat. how can i tell if she is pregnant? or is something wrong with her?
websites with pictures would help big time, or someone with experience on these little froggies:)
The reason i want to know is so that i can seperate her from the fish before she lays the eggs, so atleast the eggs have somewhat of a chance.

http://allaboutfrogs.org/info/doctor/bloat1.jpg if it looks like this it had dropsy.But other wise it would lay eggs.