So you think your ratty might be pregnant. If you got your new babies from a pet store and they were housed with males, then yes there is a 99.9 percent that she is. Here is a few pictures you can reference. As you can tell both of these soon to be mommies have pretty big bellies.
Okay, now what?
So she is deferentially pregnant. Well a rats gestation period is any where between 21 and 24 days. If she looks pretty big, I would put her in a cage on her own. When my rats are close to giving birth I either use a 10 - 20 gallon fish tank or one of the smaller hamster cages that can be purchased at most wal-marts. You should make sure she has plenty of fresh food and water at all times. You will also need to give her plenty of nesting materials, fleece, shredded up newspapers, and some of their normal bedding. Please DO NOT put toilet paper or paper towels in as nesting materials. They can get stuck to the babies while they are still wet from the birth and can dry up around their mouths and nose. Once mom has delivered the babies, go ahead and take count, and remove any dead pups. Then leave mom alone with her babies over night. Normally buy the next morning I like to check all the babies and make sure they are all eating. You can tell by looking at their milk bands, as you can see in the picture below. Normally if they don't have much of a milk band, I like to take out the ones that do and leave the others with the mom for a little bit. Not for very long tho, 10 to 15 minutes will be okay. I also like to take the babies out a little bit through out the day. Most of the time 3 to 4 times a day for 15 to 20 minutes at a time. This way mom has some time to herself, to groom herself, eat, drink and just relax. Once the babies are older you can keep them out longer.