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Screening and Treatment for Group B Streptococcus in Pregnancy ( C-Obs 19)

College Statement
C-Obs 19
1st Endorsed: July 2003
Current: July 2011
Review: July 2014

 

  1. Group B streptococcus (GBS) emerged as the leading cause of early onset neonatal sepsis in the late 1970s.1,2  Approximately 15 - 25% of women will be asymptomatic carriers of Group B streptococcus of which, if left untreated, 1 in 200 will have neonates that will develop neonatal sepsis. 3,4,5 

  2. The use of intrapartum prophylaxis with antibiotics (penicillin) given to women at risk of transmission of GBS to their newborns, prevents early onset sepsis2,6,7,8 and is cost effective.9,10 In the USA intrapartum chemoprophylaxis has led to a fall in the incidence of early onset group B streptococcal infection from 1.5:1000 (prior to screening in 1993) to 0.3:1000 in 2006.7  In Australia, intrapartum chemoprophylaxis has led to a decline in the incidence of early onset GBS disease in the past decade. 15 The incidence of late onset GBS infection (7-89 days after birth) remains unchanged.

  3. Penicillin administered to a woman with no history of β-lactam allergy has a risk of anaphylaxis of 4/10,000 to 4/100,000.7 Mortality is rare in a fully medically staffed hospital setting.  Any morbidity associated with anaphylaxis is greatly offset by reduction in incidence of neonatal and maternal sepsis. 

  4. Guidelines for prevention of early onset neonatal GBS have recommended either a risk-based or screening approach to identify pregnant women for intrapartum antibiotic prophylaxis.7,11 Practitioners should be aware of jurisdictional guidelines.

  5. Clinical risk factors for infants developing early onset disease GBS infection are:  
    • gestation ≤ 37 weeks duration,  
    • rupture of membrane ≥ 18 hours,  
    • maternal fever ≥ 38°C.  
    • previous GBS infected baby. These women should have chemoprophylaxis in subsequent pregnancies, irrespective of her current colonisation status.12 
    • GBS bacteruria (and of any count) during that pregnancy. These women should also have intrapartum chemoprophylaxis.12 
    • known carriage for Group B Strep in current pregnancy. 

  6. For the screening approach, GBS carriage is best predicted by prenatal screening at 35-37 weeks gestation [combined low vaginal and anorectal swab placed into a selective enrichment broth medium.12  Culture results are less predictive of status at term if performed at earlier gestations 13[This swab can be clinician collected or patient self-collected (see diagram)]

  7. In a large retrospective cohort study, a stronger protective effect (more cases of earlyonset disease prevented) was seen for microbiological screening of GBS colonization (culture based), as compared to the obstetric risk based prevention strategy (RR 0.46; 95% CI 0.36-0.6).12  The CDC (Centers for Disease Control, USA) have consequently concluded that culture-based strategy is superior.12  ACOG and the American College of Paediatrics recommend universal screening over risk-based screening. Where however it is impractical or inappropriate to collect swabs for assessment of GBS colonisation, it is recommended that the obstetric risk factor strategy be adopted.

  8. As screening cultures take 24-48 hours to become positive, cultures are not useful in the initial management of labour. In the future, PCR based rapid tests may become the standard of care in labour because of their high sensitivity, specificity and rapid (<1 hour) turnaround time. However, this is not yet available in routine practice in Australia and would require a 24-hour, 7-day week operating molecular biology service. 

  9. Adequate intrapartum chemoprophylaxis is defined as penicillin ≥ 4 prior hours to delivery.14 Penicillin is preferred over Ampicillin because of its’ narrower spectrum of activity, but resistance has not been observed for either Penicillin or Ampicillin. Appropriate doses for intrapartum penicillin are 1.2 gm IV benzyl penicillin loading dose, then 600 mg 4 hourly until delivery.  

  10. Among women with penicillin allergy, sensitivity testing should be requested at the time of screening culture. Approximately 20% of GBS will be resistant to clindamycin, and 30% to erythromycin.  For those women allergic to penicillin, alternative antimicrobial strategies 15 should be used in accordance with local institutional guidelines. 

  11. For elective Caesarean section (not in labour; no rupture of membranes) no prophylaxis is recommended, irrespective of carriage.12 

REFERENCES

  1. Garland SM.  Early onset neonatal group B streptococcus (GBS) infections: associated obstetric risk factors.  Aust N Z J Obstet Gynaecol. 1991; 31(2):117-118.
  2. Boyer KM, Gotoff SP.  Prevention of early on-set neonatal group B streptococcal disease with selective intrapartum chemoprophlaxis.  The New England Journal of Medicine 1986; 314:1665-1669. 
  3. Heath PT, Schuchat A.  Perinatal group B streptococcal disease. Best Practice &  Research Clinical Obstetrics and Gynaecology 2007, 21: 411-24. 
  4. Jeffery HE, Moses LM. Eight-year outcome of universal screening and intrapartum  antibiotics for maternal group B streptococcal carriers. Pediatrics 1998; 101: E2.  
  5. Gilbert GL, Hewitt MC, Turner CM, Leeder SR. Epidemiology and predictive values of risk factors for neonatal group B streptococcal sepsis. Aust N Z J Obstet Gynaecol 2002; 42: 494-503 
  6. Garland SM, Fliegner JR.  Group B streptococcus (GBS) and neonatal infections: the case for intrapartum chemoprophylaxis.  Aust N Z J Obstet & Gynaecol. 1991;31(2):119-122. 
  7. Trends in Perinatal Group B Streptococcal Disease --- United States, 2000--2006. MMWR Morb Mortal Wkly Rep 2009; 58:109.] 
  8. Early -onset group B streptococcal disease - United States, 1998-1999, Morbidity and Mortality Weekly Report, Recommendations and Reports, Centre for Disease Control & Prevention (CDC), 2000; 49:793-6. 
  9. Garland SM, Kelly N.  Early-onset neonatal group B streptococcal sepsis: economics of various prevention strategies.  Med J Aust. 1995;162(8):413-417.
  10. Prevention of Perinatal Group B Streptococcal Disease - Revised Guidelines from CDC, Morbidity and Mortality Weekly Report, Recommendations and Reports, Centre for Disease Control & Prevention (CDC), 2002, 51 (RR-11): 1-22. 
  11. Garland, SM, Starr M.  Streptococcus, group B.  In:  Management of Perinatal Infections, Australian Society for Infectious Diseases 2002. Palasanthiran P, Starr M, Jones C, eds.  Australian Society for Infectious Diseases Society (ASID).  2002:36-38. ISBN 1 74018 22 7. 
  12. Schrag SJ, Zell ER, Lynfield R, et al.  A Population-Based Comparison of Strategies to Prevent Early On-Set Group B Streptococcal Disease in Neonates.  The New England Journal of Medicine 2002; 347(4):233-239. 
  13. Yancey MK; Schuchat A; Brown LK; Ventura VL; Markenson GR. The accuracy of late antenatal screening cultures in predicting genital group B streptococcal colonization at delivery. Obstet Gynecol. 1996 Nov;88(5):811-5. 
  14. de Cueto M, Sanchez MJ, Sampedro A, et al.  Timing of intrapartum ampicillin and prevention of vertical transmission of group B streptococcus.  Obstet Gynecol. 1998; 91(1):112-4. 
  15. Johnson JR, Colombo DF, Gardner D, et al.  Optimal dosing of penicillin G in the third trimester of pregnancy for prophylaxis against group B Streptococcus.  Am J Obstet Gynecol. 2001;185(4):850-3.
  16. Prevention of Early-Onset Group B Streptococcal Disease in Newborns. ACOG Committee Opinion No. 485, April 2011.

Links to other related College Statements 

Pre-pregnancy Counselling & Antenatal screening tests (C-Obs 3)

Guidelines for consent and the provision of information regarding proposed treatment (C-Gen 2)

Resources 

RANZCOG patient information pamphlet:  Antenatal care and routine tests during pregnancy - a guide for women (July 2002)

Disclaimer

This College Statement is intended to provide general advice to Practitioners. The statement should never be relied on as a substitute for proper assessment with respect to the particular circumstances of each case and the needs of each patient.

The statement has been prepared having regard to general circumstances. It is the responsibility of each Practitioner to have regard to the particular circumstances of each case, and the application of this statement in each case. In particular, clinical management must always be responsive to the needs of the individual patient and the particular circumstances of each case.

This College statement has been prepared having regard to the information available at the time of its preparation, and each Practitioner must have regard to relevant information, research or material which may have been published or become available subsequently.

Whilst the College endeavours to ensure that College statements are accurate and current at the time of their preparation, it takes no responsibility for matters arising from changed circumstances or information or material that may have become available after the date of the statements.

 
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