I was negative with my 1st, but had decided by the time I had my 2nd that I wouldn't do antibiotics anyway so I didn't get tested. The risk of the baby getting sick without abx is about 1 in 200 or 1 in 250 depending on where you look; abx drop it to 1 in 4,000 so they do make a difference. But abx aren't without risks and side effects themselves, including an increase in the risk of other types of illnesses.
If I had to have a hospital birth again, I'd decline the test. If they wanted to give me abx I'd refuse. If they wanted to keep us for 3 days I'd sign out AMA. But you'd have to practically wrestle me into a hospital in the first place, so...
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