Screening for Group B Streptococcus Bacteria during Pregnancy Saves Lives
Prenatal screening tests are carried out at different stages in pregnancy and are extremely valuable in preventing diseases in newborns. One of the most important prenatal tests is for Group B Streptococcus (GBS). The Group B Strep screening during pregnancy is typically carried out between 35 to 37 weeks of gestation.
The newborn in the above picture, faced a life of disability because of Group B Streptococcus (GBS) infection [1]
What is GBS?
Group B Streptococcus (also referred to as Group B Strep or GBS) is a type of bacteria that causes illness in people of all ages. Group B Strep disease in newborns can lead to serious health complications such as septicemia (infection of the blood), pneumonia (infection in the lungs), and even meningitis (infection of the fluid and lining around the brain and spinal cord) within the first week of a baby's life [2, 4].
In a recent case reported by BBC News, a newborn was affected by GBS infection and faced quadriplegic cerebral palsy and lifetime disabilities [1]. However, GBS testing during pregnancy has the potential to prevent such devastating outcomes.
The timing for this prenatal GBS test is crucial for planning preventative measures. For women who are Group B Strep carriers, antibiotics given early in the pregnancy are not effective at preventing transmission during labor. This is because Strep B bacteria can reoccur after antibiotic treatment, as they are part of the natural flora in the gastrointestinal tract. From here, it is easy for the bacteria to cause reinfection.
To adequately prevent reinfection during labor, it is important for all pregnant women to be tested for Group B Strep between 35 to 37 weeks of pregnancy. If a pregnant woman’s swab sample is GBS positive, then intravenous Penicillin, Ampicillin, or Cephalosporin antibiotics are administered only during labor until delivery.
Group B Streptococcus (GBS) is a type of bacterial infection that can be found in the vagina or rectum. Women who test positive for GBS are considered colonized, and this includes about 25% of all women. Because a mother can pass GBS to her baby during delivery, this infection affects approximately 1 in every 2,000 babies in the United States. Therefore, the U.S. Centers for Disease Control (CDC), the American Academy of Pediatrics (AAP), and the American College of Obstetricians and Gynecologists (ACOG) all recommend routine GBS screening during pregnancy between 35 to 37 weeks [2].
Among babies, there are 2 main types of group B strep disease:
- Early-onset — occurs during the first week of life. Approximately 90% of cases of early-onset disease continue to manifest within the first 24 hours of life.
- Late-onset — occurs from the first week through three months of life.
Testing for isolation and differentiation of Streptococcus agalactiae (GBS) [3]
Testing Samples for Group B Streptococcus at Emery Pharma:
At Emery Pharma, we have supported clinical trials involving 200+ patient samples sent in Copan ESwab tubes for GBS screenings. The patient samples were grown in selective media, and if the sample was found to be GBS positive, the next step was serotyping of GBS-containing samples for 10 different serotypes (Ia–IX), later confirmed by a positive agglutination reaction.
A test card is used for GBS-positive serotyping, such as the one in the image above. A positive agglutination reaction is shown on the left of the figure, and a negative reaction is shown on the right.
If you would like to perform Group B Strep screenings or evaluate drug efficacy with other pathogens, contact us online or call us at +1 (510) 899-8814!
About the Author
Originally authored by Dr. Kiran Bijlani. This article was reviewed and updated on June 16, 2025 by Dr. Janet Liu, current Director of Biology.
References
- Goldberg, Adrian, 5 March 2017, BBC News-5 Live Investigates, “Newborns at risk from deadly Group B Strep bacteria”
- Center for Disease Control and Prevention, 10 July 2017 “Protect Your Baby from Group B Strep!”
- Chromagar, Dr. A. Rambach, Clinical Microbiology, CHROMagar Step B, “Isolation and differentiation of Streptococcus agalactiae (GBS)”
- Deutscher M, Lewis M, Zell ER, et al. Incidence and severity of invasive Streptococcus pneumoniae, group A Streptococcus, and group B Streptococcus infections among pregnant and postpartum women. Clin Infect Dis. 2011;53(2):114–23.
