About one in four women carry bacteria in the vagina or rectal area called group B Streptococcus (GBS). Most women do not have symptoms of GBS. If it is in the urinary tract, it may cause a bladder infection. But if passed during vaginal delivery, it can cause life-threatening infections in newborns. Every woman should get tested for Group B strep during pregnancy. If the test is positive, taking antibiotics by vein during delivery can protect the baby.

What is the Group B strep test?
The Group B strep test is a prenatal test to detect the GBS bacteria. Group B strep is not the same bacterium that causes strep throat. Strep throat is caused by Group A Streptococcus. GBS bacteria are normally found in the vagina and in the lower intestine of 15 percent to 40 percent of all healthy, adult women. Being positive for GBS is usually not serious for a woman and is easily treated with antibiotics.

If you are pregnant, though, GBS is another matter. It is known as one of the main causes of life-threatening infections in newborn babies. So, screening is needed.

Why would I need a Group B strep test?
A woman can have GBS bacteria - often in the vagina, rectum or bladder - and not know it. The bacteria usually do not cause genital symptoms or discomfort and are generally not linked with increased sexual activity. The GBS bacteria can affect the baby as it passes through the birth canal. Babies with GBS infection can develop pneumonia, sepsis (infection of the blood) or meningitis (infection of the membranes surrounding the brain).

For this reason, the Centers for Disease Control and Prevention advises that all women get routinely screened for GBS during the 35th to 37th weeks of pregnancy. Mothers who are positive should be treated with antibiotics when labor starts to protect the newborn.

Women are at high risk to pass GBS on to their babies if they:

• Start labor before they reach 37 weeks' gestation (with or without ruptured membranes)
• Reach full term, but their membranes rupture and it seems as though labor will last more than 18 hours
• Have an unexplained, mild fever during labor
• Have already had a baby who had a GBS infection
• Have or had a bladder or kidney infection that was caused by the GBS bacteria

How is the Group B strep test done?
This is a simple and painless test done via a vaginal and/or rectal swab. The swab is sent to the lab to see if the GBS bacteria grow. If it does, that shows the woman has GBS. If no bacteria grow, then the woman does not have GBS.

What if I test positive?
If you test positive for GBS bacteria, you will be treated with antibiotics when you go into labor or if your water breaks early. If you are not tested, but you are thought to be at high risk for passing the bacteria on to your baby, you also will be treated with antibiotics to eliminate the bacteria during labor and birth. Studies show it is not beneficial to give antibiotics during pregnancy. In more than 65 percent of cases, the bacteria have time to come back before labor starts.

All newborn infants are watched closely for symptoms of an infection, especially if you are GBS-positive at some point in your pregnancy, whether you are treated with antibiotics or not. Chances are small that you can pass the bacteria on to your baby if you are treated with antibiotics right before labor. But, it can still happen. Babies who show signs of a GBS infection after birth are also treated with antibiotics.

Related Articles Prenatal Visits and Routine Testing Prenatal Testing For Infectious Diseases

External Sources Duff P. Maternal and perinatal infection - bacterial. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th edition. Philadelphia, PA: Churchill Livingstone Elsevier; 2007. March of Dimes. Group B strep infection. . Accessed June 23, 2009 Centers for Disease Control and Prevention. Frequently asked questions. Group B strep prevention. . Accessed June 23, 2009

This article was reviewed and updated 08-01-2009.