I recently adopted two female spiny mice. One of them seems quite large and is bulging on her sides. The bulge moves from side to side, and her stomach feels quite firm. It's hard to feel any movement because she breathes so fast (all of my spiny mice do).
The other spiny mouse is a female for sure, too. The person I got them from claims to have never had any males, so I'm not sure what to think. Here's a photo of her bulging sides.
I took a video last night in which I could see some movement. (I can't post links or I'd love to get your opinions on that, as well). I also have photos, of which I can't post. Very frustrating to try to get some help since there are no active spiny mouse forums!