Yep, it is very common but the test results don't mean a thing because all it is, is a snapshot of THAT day - so you could have the test, get either result, but in a day or two you could be retested and get the opposite result. The only danger from it is if you are actually sick from it at the time and they will watch baby to see if they develop any signs of infection, but the chances of it are rare when you have an ab cover. Some women are told that a +ve result means they have to give birth via c/s too which isnt true.