Welcome to the site, and congratulations on your new addition to the family.
The same question about a cat being pregnant (this cat was an infoor cat who escaped for a couple days) was recently asked in another forum, and this is what one of our very knowledgable people said (he's a breeder, so he should know how to tell!
|What you should do is count from the day she returned forward 21 days. You should notice that her nipples will be a bit puffy, and pinker than usual. At 21 days, that the only way to tell... I dont think even a vet will be able to "feel" kittens yet. If you determine that she is pregnant, then she should be started on kitten food to boost her nutritional requirements. Make darn sure she doesn't get out again! If she isn't pregnant, get her spayed, that way if she does sneek out, you'll not have to worry.
Regardless, she should be taken to the vet as soon as possible to be checked out and tested for some of the nasty things that strays can pick up. Hopefully she will get a clean bill of health. The vet can also help determine approximately how old she is, and if she is pregnant.
I hope you enjoy this board as much as I have. Don't be afraid to ask any questions, no matter how simple you think they are. We all started somewhere with our knowledge about our furry angels.