Prenatal Group B Strep (GBS) Screening
- Also Known As:
- Group B Beta-hemolytic Streptococcus
- Group B Streptococcus
- Group B Strep
- GBS
- Strep Group B
- Streptococcus agalactiae
- Beta-hemolytic Strep Culture
- Formal Name:
- Prenatal Group B Streptococcus Screening

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.At a Glance
Why Get Tested?
To screen a pregnant woman for the presence of group B streptococcus (GBS) in her vagina or rectum to determine the risk that she will pass the bacteria on to her newborn during labor and delivery, possibly resulting in a serious infection in her newborn called early-onset GBS
When To Get Tested?
When a woman is between 35 and 37 weeks of pregnancy or has preterm labor or preterm premature rupture of membranes
Sample Required?
A swab obtained from the vagina and rectum of a pregnant woman; a urine sample collected anytime during pregnancy may be used to detect significant numbers of GBS.
Test Preparation Needed?
None
What is being tested?
Group B strep (GBS) is the common name for the bacterium Streptococcus agalactiae that can be present (colonizing) in the digestive tract and genital tract. It rarely causes symptoms or problems in healthy adults but can cause infections and serious illness in newborns who become infected before or during labor and delivery. GBS screening identifies the presence of the bacteria in the vaginal/rectal area of a pregnant woman.
GBS can cause early-onset GBS disease that occurs within the first week after birth. Signs and symptoms in newborns include fever, difficulty with feeding and breathing, irritability or lethargy, and a blue tint to the skin. GBS can cause serious infections such as pneumonia, sepsis, and meningitis. According to the Centers for Disease Control and Prevention, it is the most common cause of life-threatening infections in newborns.
Approximately 25% of pregnant women carry group B strep in their rectum or vagina. However, the number of infants with GBS disease has decreased significantly in recent years because of a concerted effort by healthcare practitioners to screen pregnant women for GBS late in their pregnancy and, when they are positive for GBS, to treat them with intravenous antibiotics (usually penicillin or ampicillin) during labor. This prevents or greatly decreases the risk of passing the bacteria to the newborn. Nevertheless, GBS disease remains the primary cause of early-onset sepsis, a serious and life-threatening infection in newborns.
Currently there is no vaccine available to prevent GBS, and treating all pregnant women with antibiotics is not practical. Screening for GBS and appropriate treatment continues to be the best means for preventing GBS disease in newborns.
How is the sample collected for testing?
For screening pregnant women, a swab is typically obtained from the vagina and rectum. Urine collected during pregnancy may be cultured for significant numbers of GBS.
Common Questions
Related Content
On This Site
Tests: Urine Culture; Gram Stain; Susceptibility Testing
Elsewhere On The Web
Centers for Disease Control and Prevention: Group B Strep (GBS)
Centers for Disease Control and Prevention: Get tested for group B strep (GBS)
March of Dimes Fact Sheet: Pregnancy Complications – Group B strep infection
MedlinePlus Medical Encyclopedia: Group B streptococcal septicemia of the newborn
View Sources
Sources Used in Current Review
(2016 July 11 Updated). Protect Your Baby from Group B Strep! Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/Features/GroupBStrep/. Accessed on 3/19/17.
(2016 May 23 Updated). Group B Strep (GBS), Prevention in Newborns Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/groupbstrep/about/prevention.html. Accessed on 3/19/17.
Burd, I. and Zieve, D. (2016 January 20 Updated). Group B streptococcus – pregnancy. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/patientinstructions/000511.htm. Accessed on 3/19/17.
(© 1995–2017). Group B Streptococcus (Streptococcus agalactiae) Culture. Mayo Clinic Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/87346. Accessed on 3/19/17.
Fisher, M. and Schlaberg, R. (2016 December Updated). Streptococcal Disease, Group B – Group B, Strep. ARUP Consult. Available online at https://arupconsult.com/content/streptococcal-disease-group-b. Accessed on 3/19/17.
Woods, C. and Levy, C. (2016 October 24 Updated). Streptococcus Group B Infections. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/229091-overview Accessed on 3/19/17.
Lee, K. and Zieve, D. (2014 December 12 Updated). Group B streptococcal septicemia of the newborn. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/001366.htm. Accessed on 3/19/17.
Bidgani, S. et. al. (2016 March). Comparison of group B streptococci colonization in vaginal and rectal specimens by culture method and polymerase chain reaction technique. J Chin Med Assoc. 2016 Mar;79(3):141-5. Available online at https://www.ncbi.nlm.nih.gov/pubmed/26803202. Accessed on 3/19/17.
Sources Used in Previous Reviews
Woods, C. and Levy, C. (Updated 2010 May 17). Streptococcus Group B Infections. eMedicine [On-line information] Available online at http://emedicine.medscape.com/article/229091-overview. Accessed October 2010.
Comer, Yun, H. and Hamza, H. (Updated 2010 February 11). Bacterial Infections and Pregnancy. eMedicine [On-line information] Available online at http://emedicine.medscape.com/article/235054-overview. Accessed October 2010.
Mayo Clinic Staff (2008 December 5). Group B strep MayoClinic.com [On-line information] Available online at http://www.mayoclinic.com/health/group-b-strep/DS01107/METHOD=print. Accessed October 2010.
Lee, K. and Zieve, D. (Updated 2009 December 10). Group B streptococcal septicemia of the newborn. MedlinePlus Medical Encyclopedia [On-line information] Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001366.htm. Accessed October 2010.
(Reviewed 2008 April 20). Group B Strep Prevention (GBS, baby strep, Group B streptococcal bacteria) General Public, Frequently Asked Questions. Centers for Disease Control and Prevention [On-line information]. Available online at http://www.cdc.gov/groupbstrep/about/index.html. Accessed October 2010.
Bush, L. et. al. (Revised 2009 December). Streptococcal and Enterococcal Infections. Merck Manual for Healthcare Professionals [On-line information] Available online at http://www.merck.com/mmpe/sec14/ch171/ch171d.html?qt=group b strep&alt=sh. Accessed October 2010.
(2010 March). Group B Strep Infection. March of Dimes Fact Sheet [On-line information] Available online at http://www.marchofdimes.com/professionals/14332_1205.asp. Accessed October 2010.
Forbes, B. et. al. (© 2007). Bailey & Scott’s Diagnostic Microbiology, 12th Edition: Mosby Elsevier Press, St. Louis, MO. Pp 265-279.
(November 19, 2010) Centers for Disease Control and Prevention, Morbidity and Mortality Weekly Report, Prevention of Perinatal Group B Streptococcal Disease, 59(RR10);1-32. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w. Accessed November 2010.
Centers for Disease Control and Prevention. Group B Strep (GBS). Available online at http://www.cdc.gov/groupbstrep/index.html. Accessed November 2010.
Quest Diagnostics. Streptococcus Group B Culture. Available online at http://www.questdiagnostics.com/testcenter/TestDetail.action?ntc=5617. Accessed June 2013.
Centers for Disease Control and Prevention. Fast Facts and Statistics on GBS. Available online at http://www.cdc.gov/groupbstrep/about/fast-facts.html. Accessed June 2013.
Centers for Disease Control and Prevention. Symptoms, Diagnosis, and Treatment of GBS in Newborns. Available online at http://www.cdc.gov/groupbstrep/about/symptoms-diagnosis-treatment.html. Accessed June 2013.
Centers for Disease Control and Prevention. GBS Prevention in Newborns. Available online at http://www.cdc.gov/groupbstrep/about/prevention.html. Accessed June 2013.
Bacterial Infections and Pregnancy: Group B Streptococcus. Medscape. Available online at http://emedicine.medscape.com/article/235054-overview#aw2aab6b3. Accessed June 2013.
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