How do you tell if your dog is in season?

There are no signs of pregnancy until the fifth week after mating, when the nipples become enlarged and often go a darker colour and the Dog will gain weight. It is highly unlikely that your Dog is pregnant unless she has successfully tied with an entire male at least once. Sometimes your vet will be able to do a pregnancy test to try and confirm pregnancy, but there are no simple blood or urine tests that are effective in doing this. I'm sorry but there is very little chance of knowing whether your Dog is pregnant until she is in the later stages of her pregnancy.