begoodtoanimals said:
When Harriet stands on her hind legs I see the suspicious two faint rows of belly buttons.
Actually, you're seeing nipples :lol:. Rats, don't have obvious bellybuttons once the fur comes in, and if you did see it, there would only be one and in the center of the belly

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Typically she'll become more pear shaped, and you'll know when she's about to pop because the whole belly seems to drop - it's shifting to get into position. Trust me though, you'll know she's pregnant a day or so in advance (size wise).
As for cages, I've found mom to be smart and give birth in an area that is enclosed and private. Give her an igloo and lots of nesting matterial, and switch her over to a bedd such as carefresh. You'll want to give her some fleece scraps as well. Don't give her cotton or flannel scraps, as they can fray and wrap around the babies legs. For the actual nursery tank I like to use a rubbermaid bin with 1/2 the top cover in hardware cloth. It keeps the babies warm and it only one level. Also, with the op only half open it gives mom the darkness and privacy she wants. An added bonus is that if mom is a little hostile towards you you're not trying to get at her through a tiny little door.
As for dropping the babies and killing them, let me just tell you from personal experiance - babies have a fair amount of natural bounce

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A standard litter size is around 12. My foster mom had 12, and on her next litter (people she was taken from had left the male in once the babies were born) she had 11.
You said you've had her for a week, did you get her from a petstore? Any way of knowing if she was in a mixed bin?