How can you tell when a frog is pregnant?

Can anyone tell me if my greys are pregnant or just fat? The males in their tank have been calling a lot lately, and they all just came out of a winter cycle about a month ago. I've been feeding them a lot.

Here are my females:

^ Frogger


^Weiser (left) & Frogger (right)

Thanks in advance, guys & gals!