Strep B testing goes in and out of fashion, largely because you can be tested for it, come back negative and then later get it before birth, undetected. There are signs that will indicate to your doctor that you have the Strep B infection during birth, which if detected will lead to you going on an I/V drip 4 hourly I believe. Also if you are found to be Strep B positive and you are in early labour, they are more likely to ask you to come in so they can get started on the antibiotics sooner than later.