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Mice/Pregnant Mouse


QUESTION: About 20 days ago I came home from a lovely vacation. We were having friends take care of our fish, guinea pigs, and mice. The mice which usually reside upstairs in my room were moved on the floor of the first floor for the convenience of their new temporary care takers. Bleu has always been thinner than Fern and when I came home she looked as though she gained a little bit of weight and looked a healthy weight for the first time. I joked that she was pregnant. Not a funny joke anymore. I have noticed that Bleu has been getting bigger and bigger. Fern is 100% a female mouse so she could not have impregnated Bleu. Bleu and Fern have been very busy building a nest, that I have unfortunately disturbed a couple of times thinking it was just very cute mouse behavior. Yesterday morning as I went to take them out and play with them Bleu tried to nip me. I took her out and her sides were so much larger than usual. All of this makes me believe she is pregnant. The weight gain, the nest building, and the change in her behavior (the nip).  So now I am left believing that may have been impregnated by a wild mouse who would have had a better chance of reaching her when she was on the first floor. We have in the past had mice in our basement, though she was not down there. Is it possible she could be pregnant and that a wild mouse could be the culprit? I don't know how a mouse could have gotten in but there are bars so it might be possible they mated between the bars. Does this sound at all feasible? I'll attach a picture below. I moved them into a glass aquarium with a screen on top so that if she is pregnant the babies can't get out. I put in plenty of cozy nesting material and a new nest has already been made. I'm really quite confused as to what is happening. If you have any clue it would be great to hear from you!

ANSWER: Hi Susan,

Wow, you weren't kidding, she looks very round!  It is completely possible that a wild mouse squeezed in somehow - anywhere that a mouse's head can get through, the rest of them can, and wild mice can be smaller than pet mice.

From the day a mouse becomes pregnant until she gives birth is approximately 21 days (give or take one or two days), so if she is in fact about to have babies, you should know very soon.  Most mice give birth a few hours into the night, so try not to disturb her after dark.  If she does have pups, try not to intrude on the nest for the first week and give her the space she asks for, only spot cleaning other parts of the tank if necessary, and she will keep the nest part tidy herself.  Be sure they have plenty of food and water at all times.  Baby mice take about 4 weeks to wean, at which point they'll start to figure out how to drink water on their own (they'll explore solid foods much sooner, around 2 weeks or so old).  Once they can drink reliably, they can be separated from mom (at least the boys), and you can decide what you would like to do with the babies at that point.

If, however, in a couple of weeks no babies come along, or if at any point she starts behaving lethargically or not eating/drinking, it would be time to explore some other possibilities, such as an allergy or something else causing her to bloat.  Since you do have wild mice, though, I would be really surprised if you didn't have some little ones show up very soon.

Keep me updated, and let me know if you have any other questions!

---------- FOLLOW-UP ----------

Pregnant Mouse?
Pregnant Mouse?  
QUESTION: Thanks for your speedy reply and all of your help! I greatly appreciate it! I'm getting nervous however because there are no babies yet. I have attached another picture. She is a turning in it so one side looks smaller than the other, but they are about even.  She is still eating and drinking and she has been on this food since I got her, so all is normal there. It has been 22 days since I returned home so if she doesn't give birth in the next few days I'm not quite sure what to do.

ANSWER: How long has it been since she was moved to the tank?  Even though you came back 22 days ago, could a wild mouse have gotten in a few days after?  She looks very, very pregnant to me.  If you are concerned, you can bring her to a vet who works with pocket pets - they should be able to gently palpate her sides and tell you what is going on.  I really suspect that there should be pups any day now, however.  I would only be concerned if she starts acting lethargically, eating or drinking less, or if more than a few days go by and nothing changes.

Keep me updated!

---------- FOLLOW-UP ----------

QUESTION: Thanks for all of your help throughout the past week. I have really appreciated it. I took little Bleu to the vet today and her abdomen was full of fluid so we put her down. The vet thinks it could have been a tumor that ruptured or cysts on her ovaries, but she is not really 100% sure about the cause of the fluid. She was a very sweet little mouse.
Thanks Again,

Oh no.  I am so sorry to hear this, Susan.  My thoughts are with you, and I am sorry that I gave you such hopeful news that turned out not to be the case at all.

Please let me know if I can help you out in the future with anything else, and again, I am so sorry for your loss.



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I can answer questions regarding mice as pets, mouse behavior, color and coat genetics, breeding techniques, and general health questions. I can help with caging and setup, nutrition, social issues, and what to do in most mouse emergencies (such as unplanned litters, injuries, fighting, etc.). I can also assist with questions pertaining to orphaned mouse pups, weaning litters, and questions of mating and birthing. I cannot answer questions about exotic or wild varieties of mice such as spiny or pygmy mice. *****FOR EMERGENCIES, anything requiring immediate medical intervention, PLEASE take your mouse to a professional veterinarian or wildlife rehabilitator who works with mice as soon as possible! IMPORTANT RESOURCES: Raising Orphaned Mice: Orphaned Mice Videos: Natasha's Your First Mouse: General Mouse Help: Mouse Info and Exotic Breeds:


I have enjoyed the companionship of mice nonstop since 2004, and spent a year caring for them in a lab where I learned a great deal about their breeding, social needs, and health. I spent a few years breeding them, specifically working with albinos, marked mice, angora mice, and satins. My education never stopped - I am learning something new every day from current and well-established research thanks to the wonderful folks at the Jackson Laboratory, as well as from my wonderful mousey friends online. I also love learning from my terrific questioners here on AllExperts - you folks keep my passion for these amazing animals alive and well!

East Coast Mouse Association - expired, American Fancy Rat and Mouse Association - expired

Partial University for a B.S. in Microbiology, Partial University for a 2-year degree in Veterinary Technology (RVT cert), C.E. classes in pathogens, aseptic technique, genetics, and applications

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