Group B Streptococcus

What is group B streptococcus?

Group B streptococcus (GBS) are bacteria that can be found in the digestive tract, urinary tract, and genital area of adults. Although GBS infection usually causes no problems in healthy women before pregnancy, it can cause serious illness for the mother and baby during pregnancy and after delivery.

Why is group B streptococcus a concern?

About 10 to 30 percent of pregnant women carry GBS in their rectum or vagina. In the pregnant mother, GBS infection may cause chorioamnionitis (a severe infection of the placental tissues) and postpartum (after birth) infection. Urinary tract infections caused by GBS can lead to preterm labor and birth.

Newborn babies contract the GBS during pregnancy, or from the mother's genital tract during labor and delivery. GBS is the most common cause of life-threatening infections in newborns, including pneumonia and meningitis. If a pregnant woman who is a group B strep carrier does not get antibiotics at the time of delivery, her baby has a 1 in 200 chance of developing GBS disease. Premature babies are more susceptible to GBS infection than full-term babies.

How is group B streptococcus diagnosed?

GBS can be cultured from the mother's vagina or rectum with a swab during a pelvic examination. GBS can also be cultured from a mother's urine. Cultures are usually done between 35 and 37 weeks of pregnancy and may take a few days to complete. Cultures collected earlier in pregnancy do not accurately predict whether a mother will have GBS at delivery.

Treatment for group B streptococcus:

Specific treatment for GBS will be determined by your physician based on:

  • your pregnancy, overall health, and medical history
  • extent of the disease
  • your tolerance for specific medications, procedures, or therapies
  • expectations for the course of the disease
  • your opinion or preference

A positive GBS culture means that the mother carries GBS. It does not mean that she or her baby will definitely become ill. However, the decision to treat GBS must be balanced with certain risk factors.

The Centers for Disease Control and Prevention (CDC) and the American College of Obstetricians and Gynecologists (ACOG) recommend treating women with positive GBS cultures with intravenous (IV) antibiotics during labor to reduce the risk of transmission of the infection to the baby. Treatment may also be needed for women with certain risk factors, including the following:

  • fever during labor
  • rupture of membranes (bag of waters) for 18 hours or longer
  • labor or rupture of membranes before 37 weeks gestation
  • history of GBS infection in a previous baby

How can group B streptococcus be prevented?

It is important to understand that, in spite of testing and treatment, some babies still develop GBS disease. Research is ongoing to develop vaccines to prevent GBS disease. (In the future, women who are vaccinated against GBS may make antibodies that cross the placenta and protect the baby during birth and early infancy.)

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