Not all drs and hospitals test now or routinely give ABs even if you are positive. The risk to the baby is very low and keeping a close eye on your NB should be enough to pick up if it develops an infection/fever that could be related. The need to give ABs just in case is questionable and doesn't guarantee that it will completely protect the baby anyway. Plus, ABs at birth mean you and the baby risk thrush and other complications, which can affect bfing and have potentially ongoing effects.

IMHO, A NB should be closely monitored anyway! I got tested so I and my m/ws would be aware if I was positive at the time of the test, but had no intention of taking ABs.