Pregnant molly

Question
My Mollie is trying to give birth but a very large sac is protruding with fry/eggs inside.  What is wrong?

Answer
This is a problem with livebearers as they all seem to have this affliction at some time or another. What else do you have in the tank with the mollies, how big is your tank? Are there places for the fish to hide?
Also, if its a livebearer only tank, some sea salt added to the water would benefit the fish. If its a mixed tank, ie, tetra's, cichlids or whatever then the salt should not be used.
You could isolate the molly in a protective hang on the back breeder if you have room.
There is no quick fix for this problem, you just have to try to make sure the fish is not harrassed by other fish. I wish I had a fix as this is a common issue.
Good Luck with your tank.
Mike