A version of this guide is available to download here. Free to use for personal non-commercial and voluntary use. Approx 1.5 KB. Please contact me to use any of the photos for other purposes.
Photographic guide to assessing sex and age in rodents
Featuring UK Rodents but applicable worldwide (PDF version available on downloads page)
Possible female conditions (not all shown)
Non-breeding: (also sometimes called imperforate) where a thin layer of skin forms over the vagina,
Perforate: where the vagina is open
Pregnant: indicated by a clearly distended abdomen
Has bred: Milk production indicates recent litter. Hairless halos around nipple mean she’s suckled a litter at some point (but not necessarily recently).