How to tell when Mollies are about to blow??

[Ryeguy]

Just starting up with mollies and have not had them long enough for them to give birth yet, so i do not know when she's due...and i have a pregnant calico type female (obviously) but im just wondering if anyone knows how to determine when it is time to put her into a breeding net?? She has a dark spot on her underside which i assume is the fry...BUt is there a decent way to determine when she'll give birth???...

if anyone can help it would be much appreciated

 

[WILDER]

Don't put her in a breeding net it will stress her causing her to die or abort, leave her in the tank, then remove the fry when she had them, she will be grumpy,moody, chase other fish abit and sulk in a corner,lol

 

[Ryeguy]

thanks for the help!