You can tell by taking your dog to the vet for a simple blood test, much like you would if it were yourself going to a dr. to find out if you were pregnant. I strongly advise you to make an appointment right then and there to get her spayed, just *wanting* your dog to go through a pregnancy is not enough of a reason to further the unwanted animal population in the States. There is much involved with breeding a dog, so if you are serious about this, I would firmly recommend finding yourself a breeding mentor to help you make the right choices and decisions. I truly hope you decide to get her spayed, puppies are wonderful however, it's a very dangerous and tricky business getting a dog through a pregnancy. Good luck