How do u know if your dog is pregnant?

[mamasina]

My 2 1/2 year old chocolate Lab was out in my yard, (we have to put her on a pully system because she is the master escape artist) And her b/f a mixed breed who lives 2 houses down locked onto her. We call him her b/f only as a joke. He is always trying to come over and play with her...and cocoa does the same...hence the pully system! Anyways she was very receptive to allowing him to lock. They were both in heat, I did my research and I know that there is a good chance that she may be pregnant. She wasn't fixed yet because We have a friend with a male chocolate who wanted to mate him so we were going to attempt it, only my neighbors dog beat hershey to it!!! Well my other question is If she is pregnant...which if any of the pups should we keep? Male or Female?