Way overdue pregnancy?

Question
I got a female mouse from a breeder little over three weeks ago. She tried to breed her but the mouse took forever to conceive and only had two babies at a time so she decided to retire her and adopt her out.

The breeder let me know there might be a small chance she was pregnant when I adopted her so I had that in the back of my mind. A week later I took her to the vet for an unrelated issue of an abscess and while she was being examined the vet said that she could feel babies in her tummy and I should expect them very soon. It's now three weeks in my care, the abscess has been cleared up since, she's doing a lot of nesting, excessive grooming and labored breathing like I'd expect her to and I can even feel the lumps inside her when I feel her tummy but no prebirth, no blood, no nothing yet. I believe she was removed from the male over 4 weeks ago and I suspect only one pup since I feel a body on only one side of her stomach and not the other but as time goes on with no birth in the cage, I'm starting to worry. Because she's only having one, maybe two pups she doesn't look fat but everyone who's felt her stomach feels it there. I've been limiting my handling with her and trying to give her as much privacy as possible but still nothing. What should I do?

Answer
Hi Angela,

The fact that she was having difficulty carrying full litters to term may suggest genetic problems - sometimes when lethal genetics are involved, a portion of the litter dies before birth and is reabsorbed, while the pups who did not inherit the problems survive, leading to seemingly small litters.  The reason I am bringing this up is that it seems like at this point in her pregnancy, if she has not had pups since you sent me this, we have two possibilities - one is that she is not pregnant, and could have a lump resulting from a number of other issues, or two, that she is and needs to see a vet regarding complications as soon as possible.

A normal pregnancy lasts approximately 19-21 days, but this is an estimate, and going a day or two over is certainly not unusual.  However, four weeks since her separation from the male (assuming she conceived the very last evening), puts her at a full week over her due date.  Coupled with labored breathing and no progress, this may mean she is having trouble birthing the pup or pups.  To the best of my knowledge, this is not something that can be solved at home, and you would need veterinary assistance as soon as possible to help her with the process.  It could be, also, that she is pregnant but the pups are not viable - in this case what you are feeling may be pups that have passed on and are being reabsorbed.  However, I would also recommend a vet's help in this case, too, since pups that pass away very late in pregnancy may need to be passed as stillborns instead of reabsorbed to prevent infection and illness.

The first possibility that I mentioned was that the lumpiness might not be pups, after all, but some other bump-causing problem such as a tumor, abscess, or fatty growth.  If you already treated for an abscess and had success, I would think this cause might be unlikely, but tumors can certainly occur anywhere in the body and would feel like a small lump.  Tumors are honestly a lot less scary than they sound, and they don't mean your mouse will die of cancer or anything - they just mean she'll be a little bumpy, is all.

However, it's impossible to tell which of these possibilities is causing her current state, and with her labored breathing, I really recommend a vet as your first course of action if she has not already given birth.  It's a good idea to bring her entire cage in to reduce stress as much as you can.

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