This is a complicated question to answer in a short space, but I'll try to be succinct. It's true that many pregnant women harbor these bacteria in their lower genital tract or rectum; infections such as this are actually more common in pregnancy. A problem arises if the pregnant woman develops a major infection in the uterus during her pregnancy (in which case she would develop a fever and be quite sick) or if she passes the bacteria to the baby during the birth itself. Group B streptococcus (GBS) in a newborn can have devastating results. You were tested and found positive. You were probably treated with antibiotics as well. Although this would seem to be the best thing for protecting a fetus, unfortunately it does not always work. Many women who are treated while pregnant become "re-colonized" later. The American Academy of Pediatrics (AAP) recommends that all pregnant women should be screened for GBS, and colonized women should be treated with intravenous (IV) antibiotics at the time of labor so there is no chance that the baby will contract the disease while it is being born. The American College of Obstetricians and Gynecologists (ACOG) suggests that only women who have risk factors be screened in pregnancy, but agrees with the AAP that women who test positive should be treated during labor. How did you get it? It's anyone's guess. GBS is a common infection. The important thing is that you know that you have tested positive, and that you get treatment by IV when you are in labor. Be sure that whoever is taking care of you in labor knows all about this.