Treatment of Group B Streptococcus in Pregnancy
All pregnant women who are GBS carriers (identified by vaginal-rectal culture at 35-37 weeks' gestation) must receive intravenous antibiotic prophylaxis during active labor, not before. 1
Screening Protocol
Screen all pregnant women at 36 0/7 to 37 6/7 weeks' gestation with vaginal-rectal culture. 1, 2 The optimal collection method involves swabbing the lower vagina first, then inserting the same swab through the anal sphincter into the rectum—do not use speculum examination. 1, 2 Specimens should be inoculated into selective broth medium (SBM or Lim broth), incubated overnight, then subcultured onto blood agar. 1
Intrapartum Antibiotic Prophylaxis Regimens
For Women Without Penicillin Allergy
Penicillin G is the preferred agent: 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery. 1, 2 Penicillin G is preferred over ampicillin because its narrow spectrum reduces selection pressure for antibiotic-resistant organisms. 1
Ampicillin is an acceptable alternative: 2 g IV initially, then 1 g IV every 4 hours until delivery. 1
For Women With Penicillin Allergy (Not High-Risk for Anaphylaxis)
Cefazolin is the preferred alternative: 2 g IV initially, then 1 g IV every 8 hours until delivery. 1, 2 Approximately 10% of penicillin-allergic patients cross-react with cephalosporins, so careful allergy history is essential. 2, 3
For Women at High Risk for Anaphylaxis
High-risk features include history of anaphylaxis, angioedema, urticaria to penicillin, or asthma that would make anaphylaxis more dangerous. 1, 2
If GBS isolate is susceptible to clindamycin: Clindamycin 900 mg IV every 8 hours until delivery. 1, 2 Susceptibility testing for clindamycin and erythromycin must be performed, as clindamycin resistance ranges from 3-15% among GBS isolates. 2
If susceptibility unknown or resistant to clindamycin: Vancomycin 1 g IV every 12 hours until delivery. 1, 2
Critical Timing Considerations
Administer antibiotics at least 4 hours before delivery for maximum effectiveness. 1, 2 When given ≥4 hours before delivery, intrapartum prophylaxis achieves 78-80% reduction in early-onset neonatal GBS disease. 2, 4, 5 Even shorter durations achieve therapeutic levels, but 4 hours is optimal. 1
Special Clinical Scenarios
GBS Bacteriuria During Pregnancy
Any concentration of GBS in urine at any point during pregnancy requires immediate treatment of the UTI AND mandatory intrapartum IV prophylaxis during labor, regardless of whether the UTI was treated earlier. 1, 2 GBS bacteriuria indicates heavy genital tract colonization and significantly increases risk of early-onset neonatal disease. 2 Women with documented GBS bacteriuria should not be re-screened at 35-37 weeks—they automatically qualify for intrapartum prophylaxis. 2
Preterm Labor (<37 Weeks)
If GBS status unknown, obtain vaginal-rectal culture immediately and start GBS prophylaxis. 1 Continue prophylaxis until delivery if true labor progresses. 1 If not in true labor, discontinue prophylaxis and repeat screening at 35-37 weeks if patient has not delivered. 1
Preterm Premature Rupture of Membranes (PPROM)
Ampicillin 2 g IV once, followed by 1 g IV every 6 hours for at least 48 hours provides adequate coverage for both latency and GBS prophylaxis. 1 If other latency regimens are used, add separate GBS prophylaxis. 1
Unknown GBS Status at Labor Onset
Administer intrapartum prophylaxis if any of these risk factors are present: 1
- Gestational age <37 weeks
- Membrane rupture ≥18 hours
- Intrapartum temperature ≥100.4°F (≥38.0°C)
Planned Cesarean Delivery
Women undergoing planned cesarean delivery before labor onset and before membrane rupture do NOT need intrapartum GBS prophylaxis. 2, 6
What NOT to Do: Common Dangerous Pitfalls
Never treat asymptomatic GBS vaginal colonization with oral or IV antibiotics before labor. 1, 2, 6 This approach is completely ineffective at eliminating carriage, does not prevent neonatal disease, promotes antibiotic resistance, and may cause adverse drug effects. 1, 2, 6 This is a Grade D-I recommendation (evidence supports NOT doing this intervention). 6
Do not assume that treating a GBS UTI earlier in pregnancy eliminates the need for intrapartum prophylaxis. 2 Recolonization after oral antibiotics is typical, which is why intrapartum IV prophylaxis remains mandatory even if bacteriuria was treated months earlier. 2
Erythromycin is no longer acceptable for intrapartum GBS prophylaxis in penicillin-allergic women. 1 Resistance rates are too high. 1
Do not use fluoroquinolones like ciprofloxacin for GBS prophylaxis—they are not validated for this indication. 3
Neonatal Management
Routine prophylactic antibiotics for infants born to mothers who received intrapartum prophylaxis are not recommended. 1 However, any newborn with signs of sepsis should receive full diagnostic evaluation (blood culture, CBC with differential, chest radiograph if respiratory signs present, lumbar puncture if stable) and empiric antibiotic therapy including IV ampicillin. 1
Well-appearing newborns whose mothers had suspected chorioamnionitis should undergo limited evaluation (blood culture and CBC) and receive antibiotics pending culture results. 1
Risk of Anaphylaxis
The estimated frequency of anaphylactic reactions to penicillin is approximately 5 per 10,000 treatments, which can have severe consequences for both mother and child. 7 This risk must be balanced against the substantial benefit of preventing early-onset neonatal GBS disease, which has decreased by more than 80% since implementation of universal screening and intrapartum prophylaxis strategies. 4