For more information on breeding rats yourself, click here , for the breeding page. In my experience, however, I didn't know my rat, Whiskers, was pregnant until she delivered. You see, I was 7 at the time. There are several signs that may lead you to the conclusion that your rat is pregnant. Two weeks into the pregnancy, the females waist will start to expand, and towards the end you may see the ratlets moving around inside of her.
Expectant mothers tend to make larger nests a few days before the birth.
The gestation period, or days while the rat is pregnant, is anywhere from 21 to 23 days, but I have heard of it being 24 days, also. During this time, you should provide the female with extra food and some extra bedding. If you've got a male that lives with the female, you should remove him before the birth. According to Debbie Ducummon, he would never hurt his babies. However, the female could become pregnant again within 24 hours of the birth.