rat soon to give birth

Question
I have a female rat who i believe is pregnant. Iv been weighing her and so far i think she's gained about 3 ounces, but my scale is extremely innacurate. So my first question is, how can i know for sure? Anyway, if she is pregnant she should be giving birth any day now. I've prepared a special cage for her to give birth in, but she seems so lonely in there. She is use to a large two level cage with a friend, and i feel bad isolating her. Should i leave her with her friend in the big cage until right before birth, or should i just put her in the smaller cage to give her time to get use to it? Websites say i should put her in the smaller cage a few days before delivery, but she just seems so sad all alone. Any suggestions?

I have done hours of research to make sure im doing everything right for her, but i'm still open to any advice i can get. I just really want everything to go smoothly for my little girl.

Answer
 The gestation period of a rat is 23 days, which I'm sure you've already discovered, so if she is apart from a male for at least 25 days and doesn't give birth, she isn't pregnant.  Though usually a pregnant rat's tummy swells and makes the pregnancy fairly obvious, if there aren't very many babies sometimes they can look completely normal until they give birth.  A few days before the birth the hair will fall out around her nipples, which will make them more prominent.  She will also exhibit nesting behaviour, though sometimes they don't make a nest until after the babies are born.

 About whether or not to separate them, it's up to you and how well your rats get along.  Rats in the wild raise their babies together and will take turns nursing and cleaning the babies and can be very loving to another rat's babies.  In captivity, though, it can cause some problems.  The other female may try to take care of the babies even though she can't nurse them, and female rats can sometimes get into a tug-of-war over the babies, hurting them in the process.  The mother may be very protective of her babies and it may cause them to fight.

 If you want to try leaving the girls together you can, they will likely be fine, but you need to be mindful of the problems that can occur and make sure you are able to remove her quickly if there are any altercations.

 If you do decide to separate her, it's good to give her at least 5 days or so in the small cage before the birth so she can have time to get used to it, make a suitable nest, and feel comfortable there so she can give birth without worry.

 Well I hope that helps answer your questions, good luck with your rats!