Pregnancy Information Center

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Group B Strep: What Pregnant Women Need to Know


Learn about group B strep testing and treatment

By Elaine Brown, MD

What Is Group B Streptococcus?

Prior to the mid 1960s, group B streptococcal (GBS) infections in people were almost unheard of. Unfortunately by the mid 1970s, there had been a meteoric increase in the number of reported cases. Worst of all, the infections were occurring in pregnant women and their newborns, with fatality rates of 20 to 50%.

GBS is a type of bacteria that typically colonizes the vagina and lower gastrointestinal (GI) tract of women. It is likely that virtually every woman is colonized by GBS at some point in her lifetime. Approximately 20 to 30% of all pregnant women are carriers at any given point in time. Colonization (meaning that the bacteria is detectable on swabs taken from the vagina or lower GI tract) can be transient, it can be intermittent or it can be chronic. A woman may test positive in one pregnancy but negative in the next. Being a carrier is different from having an infection because a carrier has no symptoms. GBS is not considered to be a sexually transmitted infection.

To determine whether a mother is a carrier, a swab is taken from the vagina and/or rectum of the pregnant mother. This test should be performed in all mothers-to-be between 35 to 37 weeks gestation, or on any mothers who are admitted with preterm contractions.


Infections Caused by Group B Strep

In newborns, GBS infections are divided into two groups: early onset and late onset.

In newborns, early onset cases occur within the first week of life, with most cases diagnosed on the day of the baby's birth or within 72 hours. Late onset cases occur after the first week of life. Meningitis (infection of the spinal fluid) is diagnosed in up to one-third of late onset cases and permanent neurologic injury can follow. GBS can cause infection in the blood, lungs, brain, or spinal fluid of the baby, or it can result in milder infections, of the skin, for example. Skin infections may be referred to as erysipelas.

In mothers, GBS causes urinary tract infections, infection of the placenta and membranes during labor, infection of the uterus after delivery or infection of the blood (known as bacteremia).

Group B strep infections can be very successfully treated with antibiotics, especially penicillin or ampicillin. Prevention of the infection is preferable, however, and several strategies have been developed for this purpose. Presently all women are tested just before their due date, and if they are current carriers (have a positive test), they are given antibiotics while they are in labor, unless a C-section is planned. Women who have had a urinary tract infection caused by GBS during their pregnancy and mothers who have had a baby with GBS in the past are also treated. Women with preterm contractions are treated with antibiotics until their culture results are available (usually within 48 hours).

The new universal testing approach has been quite successful — since the 1990s there has been an approximately 80% decrease in early-onset GBS infections in newborn babies.

In the future, hospitals may switch to a rapid test for group B strep that can be obtained from the mother when she is in labor. Tests for GBS that give immediate results are in the pipeline and already in use in some institutions. Doing the test at the time of labor would be a better strategy because a mother may be positive at 35 weeks but negative at 40 weeks when the baby is born, or more importantly, the opposite could be true. With the rapid test, mothers who are negative at the time of delivery would not be exposed to antibiotics, which are typically very safe, but can cause allergic reactions. And mothers who have become new carriers during this time frame would not be missed.

Another exciting development is a vaccine against GBS, which may soon be used in young teens to immunize them against GBS — similar to the way that the HPV vaccine (Gardasil) is currently used.

Continued efforts are being made to protect women and infants from the devastating effects of group B strep. There is very real hope that in the near future, GBS disease will be a thing of the past.

Dr. Elaine Brown completed her residency in obstetrics and gynecology at Harvard. She has more than 15 years of experience in private practice.


Published March 6, 2014



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Reviewed by Elaine Brown, MD on February 9, 2014