signs of pregnancy with a sailfin molly

I have a male and female pair of sailfin mollies, I've noticed that the female's belly has gotten bigger and I can see a few black spots inside of her tummy. However I've noticed these two signs for several weeks with no dramatic changes. Since I'm unsure of molly's pregnant signs and length of gestation I was wondering if someone could give me some insight? Thanks

I saw Crr's thread, but I'm wondering if anyone can discribe the signs of pregnancy in a sailfin (ie:non-balloon) molly. Also does anyone know how long a typical pregnancy lasts for these fish?