GBS is one of many types of streptococcal bacteria. Another common type of streptococcus is group A streptococcus, which causes strep throat.

GBS is diagnosed by culture, which requires 48 hours to complete. Ideally, the culture should be done at a prenatal visit between 35 and 37 weeks of gestation.

CAUSE OF INFECTION:

GBS is commonly found in the gastrointestinal and genital tracts. For healthy adults, the bacterium is not harmful and does not cause problems. In pregnant women and newborn infants, however, GBS infection can cause significant illness.

A person who carries GBS is said to be colonized with the bacteria. Colonization can be temporary, can come and go, or can be chronic. GBS colonization is not harmful and should not be treated, except during labor and delivery.

Between 5 and 40 percent of women (both pregnant and nonpregnant) are colonized with GBS. Although GBS is not a sexually transmitted disease, a person can become colonized during sexual activity. Babies can become colonized from bacteria that are transmitted during labor and delivery and by handling the infant after birth.

COMPLICATIONS:

Pregnancy complications — There is increasing evidence that women who have large amounts of GBS in the vagina and urinary bladder are at a higher risk for developing chorioamnionitis, an infection of the membranes surrounding the fetus. This can lead to premature labor or premature rupture of membranes and preterm delivery.

A urine culture is commonly performed at the first prenatal visit, even for women with no symptoms of urinary tract infection. GBS urinary tract infections, even in pregnant women who have no signs or symptoms (eg, painful, frequent urination) increase the risk of preterm birth. Antibiotics are recommended if a woman's clean catch urine culture shows evidence of infection. Following treatment, a repeat urine culture is recommend to ensure that the infection in the bladder has been eliminated.

Risk factors — Pregnant women are susceptible to infection of the membranes surrounding the fetus (chorioamnionitis), particularly if her water breaks early (several hours or days before birth).

Postpartum complications — A woman can also develop infection related to GBS after delivery. Signs of infection can include fever (often within 12 hours of delivery) and chills, uterine pain and/or a distended abdomen. In rare and severe cases, the infection can spread to the blood (septicemia). Postpartum infections are treated with intravenous antibiotics.

PREVENTION AND TREATMENT:

GBS culture — Expert groups recommend that all pregnant women have a GBS culture of the vagina and rectum at 35 to 37 weeks of gestation. This is not necessary if the woman had GBS in a urine culture earlier in the current pregnancy or for women who previously had an infant with GBS infection; these women should always be given antibiotics during labor and delivery.

Cultures taken at 35 to 37 weeks of gestation can predict if GBS colonization is likely during labor and delivery. Cultures done more than five weeks before delivery are less reliable for predicting GBS colonization at delivery.

Antibiotic treatment — The American Academy of Pediatrics, American College of Obstetricians and Gynecologists, and Centers for Disease Control and Prevention all recommend antibiotics during labor for all GBS colonized pregnant women.

If a woman has a positive GBS culture and is allergic to penicillin (eg, there is a risk of a life-threatening reaction), she should be sure that her clinician is aware of this allergy. An additional test may be needed to determine which antibiotic should be used during labor.

Benefits — Antibiotics given in labor reduce the chance of early-onset neonatal infection 30-fold. If antibiotics are not given to a GBS-colonized woman at term who has no other risk factors (eg, fever, prolonged membrane rupture), there is a 1 in 200 chance of neonatal GBS infection; this risk drops to 1 in 4000 if antibiotics are given.