Can she be pregnant?

Question
Hi I bought a mouse for my daughter about a week ago and all was fine.
I have noticed some behavioral changes in her. She is squeezing every time I picked her up and if I try to pat her
She attacks me. Mainly around her stomach. Just wondering if she could be pregnant. The pet shop said that she was mixed with makes when she first came in. I did buy a male to mate with her but that was only today. If she is pregnant that is great. I just want to make sure that this is the reason she could be aggressive. Don't want to let my daughter hold her.

Answer
Hi Yvonne,

Mice have a gestation period of about 21 days, so depending on when the pet shop separated her, she would likely be fast approaching her due date.  For that reason, you may want to reconsider keeping a male in the cage with her right now - males do not always make good dads and can kill the pups, in addition to potentially getting her pregnant again immediately.  A back-to-back pregnancy would not only put mom at risk, but the second litter as well, since the first pups would still be nursing when the next ones were born.  One more thing to consider is health - it's a good idea to isolate new mice for 2-3 weeks on arrival before breeding so a seemingly healthy mouse does not accidentally bring an illness back from the pet shop, since pregnant and nursing mice cannot be given antibiotics if they get sick.

With all that aside, I have never known a mouse to become more aggressive during pregnancy.  Stressed mommas may become protective once the mice are born, but not before.  Be cautious in your breeding - this fearful aggression may be temporary as she adjusts, but it would be unwise to risk passing an anxious temperament to future generations until you know if she can be happy just being your pet.  I am unsure what you mean by squeezing?  The stomach area is a vulnerable part of the body, and since you haven't had her very long, she could be jumpy about how she is handled.  A good way to safely lift her is by scooping up a toy (but not her hide or "safe space") and letting her walk onto you, or, if done carefully, to pick her up by the middle of her tail and place her on your flat hand.  Never lift by the tip or base of the tail, and never suspend a mouse this way - it should be a calm, swift transition lasting 1-2 seconds.  Also never pull on her tail if she grabs something in the cage - just give her some space and try again later.

I think after a little time and respectful handling, and by removing the stress that is constantly being pursued by a male, she should warm up to you both soon.  Mice just need a little patience when they first come home.

Best of luck, and let me know if I can help with anything else!
-Tam