I tested positive with DD1, heavy growth. My waters broke before contractions so I was in straight away. They give them through a canula in your hand which I didn't feel at all (nor later when I tore it out) because who notices when you're in labour ay . I believe they give them every 4 hours or so through labour especially once your waters are broken since that's the highest infection time. I only needed the one dose as only had 4 hour labour with DD1. My mums waters broke before her birth with both my brothers, and both got severe respiratory infections attributed to that time and were in the SCN for a couple of weeks. These days the AB's would likely have prevented that in her cases, though probably like everything these days in most cases it wouldn't matter KWIM. I was negative with DD2 so did nothing.