:
I know the infection is transient and ditto what Traveller said, but I *think* the risks to baby if you are GBS positive, whilst low, can be quite deadly. I might be confused on this though - I'm sure there's heaps of accurate information available if you research it.
You are quite correct, GBS can be very dangerous for a baby and can cause life threatening sepsis. If you or the baby test positive for GBS around birth but are asymptomatic the effects of antibiotics on a fragile gut must be weighed against the small chance of the child developing sepsis.

It's a decision that only you can make, I'm not sure what I would do in your situation having had a child with sepsis (albeit from an entirely different infection).