An excerpt from The Birth Center Client Manual
GBS is a type of bacteria that can be found in up to 40% of pregnant women. A woman with GBS can pass it on to her baby during delivery—most babies who get GBS do not have any problems: a few, though, may become seriously ill. Because of this, all women are tested for GBS at 36 weeks via vaginal swab. For those who test positive, IV antibiotics are given during labor so that the risk of GBS being passed to the baby is decreased.
The American College of Nurse Midwives provides answers to some FAQs here. Interested in more information about GBS? Click here for guidelines from the CDC.