Group B Streptococcus is a bacterium that lives in the vaginal area of some women. While it normally does not cause any health problems for the woman, it can migrate up into the uterus during labor after the bag of waters has broken and infect both the newborn infant and the mother. It is for this reason that IV antibiotics are given during labor to women who are Strep positive. The antibiotics suppress or kill the bacteria so they do not infect the newborn or the mom. The longer a woman is in labor after the water breaks, the more chance the Strep has to get into the uterus and cause infection. It is generally felt that if more than 12 to 18 hours passes after the water breaks, this greatly increases the chance of infection. If, on the other hand, less than 12 hours passes, the chance of infection is minimal. In addition, if a mom has a fever over 101 during labor, this is a concerning sign that the Strep may have migrated into the uterus.
Some obstetricians and midwives choose to not test women for Strep. Instead, they will give IV antibiotics if a mom has fever during labor or if labor continues more than 12 to 18 hours after the water breaks.
The Strep bacteria often do not continuously live in the vaginal area. They usually come and go, so if a woman tests positive with one pregnancy, it is generally assumed that she will always be intermittently positive throughout her life. She is therefore treated as positive during subsequent pregnancies.
This Strep is not the same strep as the one that causes sore throats. They are completely unrelated.