Guppy Mothers Not Giving Birth

[OrkyBetta]

I have two guppies that I bought pregnant, and I really have no idea how long I've had them. They look heavily pregnant, with a gravid spot on each, but they have been pregnant for a long, long time. They are both in their own seperate tanks, and I am baffled as to why they arent giving birth. Can anyone help?

 

[IovaykInD]

Tank size? How long has it been set up? It might be because the females are stressed so they don't think the water conditions are good enough to let the fry out. Female guppies are able to hold their fry in for a very long time, just because they don't think the water conditions are good.