HELP! Could my mouse be pregnant?

Question
Hello =]
I recently brought two "female" mice from my local pet store. When i brought them they were much the same size. Recently i noticed one of the mice has balloned in a matter of days. i tried sexing the mice from pictures i found on the internet and, to the best of my ability, they look to be both female =S. they are only 4 and a half months old approximatly. I brought them at 10 weeks old. the bigger mouse is only big around her belly though and her legs seem to be the same size as they were when we got her. Could my mouse be pregnant?
thankyou

Answer
Dear Danni,

If it has been less than 3 weeks since you bought the mice, she came pregnant from the pet store.  Pet stores are notorious for making this kind of mistake.  You're lucky the other one isn't pregnant too!

If it has been longer than 3 weeks, then you either have a male or you have a wire cage and a wild mouse got in.

Have fun with the babies!  There are a ton of posts on here where I write about raising baby mice.

squeaks n giggles,

Natasha