How to tell?

Question
We recently, about 1 month ago, got 2 female guinea pigs. We think one is pregnat, they were kept in the same cage as their brother in the pet store. How can we tell for sure if she is and if she is will it be ok to leave the 2 females together in the cage during child birth and rearing?

Answer
You could always take her to the vet if you are unsure. But as time passes there will be signs. She will start to round out and become bigger. If the cage is large enough you can leave them together for now, but when the babies are born they will need their own space.