Unfortunately there really isn't any way to "know" what you want to know.

You'll know when you know, no?

-andy

Your molly will really look hugs - like she's about to burst! And then she'll look a bit squarish huge. How many babies is pretty hard to say! I do know that with female mollies I've had - sometimes they'll find a nice little sheltered/hiding place towards the bottom of the tank when they're giving birth.