Pregnant Mice??

Question
Hey Tamarah,

Not sure if you remember, but I asked you a question about a week ago about my 2 original mice and then my addition - Mocha. I ended up taking Mocha back, because he just made my cage smell so bad. i didn't mind if he got the other females pregnant because I really want a litter of baby mice.
When I took him back to the pet shop, they happily swapped him and I bought another mouse so that she would have one of her original cage mates to play with.
One of the new mice I bought, seems to have gotten a bit bigger than her original cage mate, with a larger 'band' area around her stomach. When she is on her wheel and is getting off, with her 2 front feet on the floor and her back feet on the wheel, you can see a groove where her spine is, and then it kind of bulges on the sides of it. This makes me think that she's just not fat because otherwise it would be on top of the spine too? And when she is sitting still, she looks kind of plump while the other one I bought at the same time still looks really small.
The pet shop does keep males and females together, is pregnancy a high or low possibility?

Thanks,
Claire

Answer
Hi Claire,

Of course I remember!  I'm sorry you had to return Mocha, but I'm glad you found a couple of new friends.  :)

ANY time males and females are together there is the possibility of pregnancy.  The only way to know is to wait - gestation in mice is approximately 3 weeks.  If you've had her for 3 weeks and you don't get any babies, she may still be growing.  Most pet shops sell mice before they are full grown, so they do typically put on a little weight as they mature.  Mice are not full grown or ready to have low-risk pregnancies until 3 months of age, which is something to carefully consider when allowing males and females together in your home, even if you want a litter.  Not only does risk go up when the females are not fully developed themselves, but as I may have mentioned before, they also cannot be treated for any new diseases with normal antibiotics while pregnant or nursing.  For this reason, isolation of all new mice is very, very important, whether they are pregnant or not, and of either gender.

Best of luck on your possible new litter, and congratulations on your new mice!  :)
-Tam