I had a thread about this when TTC #2.

With DD I literally had just a small amount of brown blood when wiping. It was once only.

With this pregnancy I had brown and red blood off and on for about 4 days. I would think it was getting heavy (and therefore AF) and make necessary 'preparations' but would then find nothing else there. Since it happened for so long I honestly thought it was a light AF. If I hadn't have tested I probably wouldn't have found out for another month as I had no symptoms this pregnancy either!