I have 4 that seem to be expecting already. I'm pretty sure they were seperated at the store (they came from the back room, but ive been back there before and im pretty sure they have males and females in seperate tanks). I've read that as early as 7-10 days the babies can be felt in them. I cant really feel these, because the mice are still a little jumpy and wont cooperate, but I can see lumps if i hold them up by the tail. I'm guessing in about 2 more weeks ill have my first litter. I guess I have till then to decide what I'm going to do with them all. I dont really need anything larger than pinkeys right now, but i hate to gas and freeze all of my first litter. I may keep a few and if any of my current females arent giving good sized litters, or taking good care of the babies i may replace it with one of them.