What are the guidelines for Group B Streptococcus (GBS) screening in pregnancy?

Guidelines for Group B Streptococcus (GBS) Screening in Pregnancy

All pregnant women should be screened for GBS colonization with vaginal and rectal cultures at 35-37 weeks' gestation to identify candidates for intrapartum antibiotic prophylaxis. 1

Universal Screening Recommendations

• Screening should be performed between 35-37 weeks' gestation with both vaginal and rectal specimens collected during the same examination 1
• A single swab (or two different swabs) should be used to collect specimens first from the lower vagina (vaginal introitus) and then from the rectum (insert swab through the anal sphincter) 1
• Specimens should be placed in a nonnutritive transport medium and properly labeled for GBS testing 1
• Specimens should undergo 1-4 hour incubation at 35°-37°C in an appropriate enrichment broth medium to enhance GBS recovery 1
• For women with penicillin allergy at high risk for anaphylaxis, antimicrobial susceptibility testing should be performed on antenatal GBS isolates 1

Indications for Intrapartum Antibiotic Prophylaxis

Prophylaxis Indicated:

• Previous infant with invasive GBS disease 1
• GBS bacteriuria during any trimester of the current pregnancy 1
• Positive GBS vaginal-rectal screening culture in late gestation during current pregnancy 1
• Unknown GBS status at the onset of labor (culture not done, incomplete, or results unknown) with any of the following:
  • Delivery at <37 weeks' gestation
  • Amniotic membrane rupture ≥18 hours
  • Intrapartum temperature ≥100.4°F (≥38.0°C)
  • Intrapartum nucleic acid amplification test (NAAT) positive for GBS 1

Prophylaxis NOT Indicated:

• Colonization with GBS during a previous pregnancy (unless an indication for GBS prophylaxis is present for current pregnancy) 1
• GBS bacteriuria during previous pregnancy (unless an indication for GBS prophylaxis is present for current pregnancy) 1
• Negative vaginal and rectal GBS screening culture in late gestation during the current pregnancy, regardless of intrapartum risk factors 1
• Cesarean delivery performed before onset of labor on a woman with intact amniotic membranes, regardless of GBS colonization status or gestational age 1

Management of Special Situations

Threatened Preterm Delivery

• Women admitted with signs and symptoms of preterm labor (<37 weeks) should be screened for GBS colonization at hospital admission unless a vaginal-rectal GBS screen was performed within the preceding 5 weeks 1
• Women with preterm labor and unknown GBS status should receive GBS prophylaxis at hospital admission 1
• If not in true labor, GBS prophylaxis should be discontinued 1
• If GBS culture becomes available and is negative, GBS prophylaxis can be discontinued 1

Preterm Premature Rupture of Membranes (PPROM)

• Obtain vaginal-rectal swab for GBS culture and start antibiotics for latency or GBS prophylaxis 1
• If receiving antibiotics for latency that include ampicillin 2g IV once, followed by 1g IV every 6 hours for at least 48 hours, this is adequate for GBS prophylaxis 1
• If other antibiotic regimens are used, GBS prophylaxis should be initiated in addition 1

GBS in Urine

• Women with GBS isolated from the urine in any concentration during their current pregnancy should receive intrapartum antibiotic prophylaxis 1, 2
• GBS bacteriuria should be treated according to current standards of care for urinary tract infection during pregnancy 1, 2
• Women with GBS bacteriuria do not need additional GBS screening at 35-37 weeks' gestation 2

Antibiotic Prophylaxis Regimens

• Penicillin remains the agent of choice for intrapartum antibiotic prophylaxis, with ampicillin as an acceptable alternative 1
• For women with penicillin allergy without history of anaphylaxis, angioedema, respiratory distress, or urticaria, cefazolin is recommended 1
• For women with high risk for anaphylaxis, clindamycin is recommended if the GBS isolate is susceptible to clindamycin and erythromycin 1

Common Pitfalls and Caveats

• Performing only vaginal cultures without rectal cultures can miss approximately 18.5% of GBS colonization cases 3
• Antimicrobial agents should not be used before the intrapartum period to eradicate GBS colonization, as this is ineffective and can cause adverse consequences 1, 2
• A negative GBS screen is considered valid for only 5 weeks 1
• Despite screening efforts, early-onset GBS disease still occurs, with studies showing 60-80% of cases occurring in neonates with negative maternal screening during pregnancy 4
• Recent updates from ACOG recommend performing universal GBS screening between 36 0/7 and 37 6/7 weeks of gestation, which is a slight change from previous CDC guidelines 5

By following these guidelines, the incidence of early-onset GBS disease has declined dramatically, though it remains a leading cause of neonatal morbidity and mortality requiring continued vigilance 6, 7.