I am 8 months pregnant, and at my checkup yesterday my doctor told me I had strep in my vagina. He didn't explain what that means or how I got this infection, but I do know that it can harm my baby! Can you please tell me more?

--Rene

Group B streptococcus (GBS) lives in the vagina and rectum of between 10 and 30 percent of pregnant women. Most of the time it does not cause any symptoms or problems in the woman, although it may cause a urinary tract infection. During labor and delivery, GBS may be transmitted to the baby. In full-term babies it usually does not cause severe illness, but it is a much more serious problem in premature babies. In the United States, GBS infection occurs in newborns at a rate of nearly two in every 1,000 live births, and in about 6 percent of cases, it proves fatal.

Several factors increase the chance that your baby will develop a GBS infection. These include giving birth prematurely, giving birth more than 18 hours after your membranes rupture, having a fever during labor, having GBS in your urine, or having a previous baby affected with GBS.

Doctors can minimize the chance of severe GBS infection in the baby by treating all women with known GBS or one of the above risk factors (prolonged rupture of the membranes, premature labor, history of prior child with GBS, etc.) with antibiotics during labor. Treatment earlier in pregnancy is not effective, as in many women the GBS comes back. Penicillin or its derivatives are the treatment of choice; a dose is given every four hours through an intravenous line until delivery occurs. This approach can reduce the rate of GBS infections in newborns by 70-90 percent.