Immediate IV Penicillin Administration
Administer IV penicillin G as soon as possible upon admission to labor and delivery—this is the correct answer (Option C). 1, 2
Rationale for Intravenous Antibiotic Prophylaxis
The CDC and ACOG explicitly recommend that all GBS-positive women receive intrapartum antibiotic prophylaxis when labor begins, regardless of whether they received any prior treatment. 1, 2
The positive GBS screen at 34 weeks remains valid at 36/37 weeks since screening cultures are considered valid for 5 weeks from collection, and this patient is only 2-3 weeks beyond her positive test. 1, 2
Effective prophylaxis requires intravenous administration to achieve adequate tissue and fetal blood levels—oral antibiotics are insufficient. 1
Why the Other Options Are Wrong
Option A (Immediate C-section) is incorrect:
- Cesarean delivery is NOT indicated solely for GBS prophylaxis. 1
- The CDC specifically states that intrapartum prophylaxis is not routinely recommended only for cesarean deliveries performed before labor onset with intact membranes. 1
- Since this patient is already in labor, vaginal delivery with appropriate antibiotic coverage is the standard approach. 1, 2
Option B (Single dose oral amoxicillin) is incorrect:
- Antepartum oral antibiotic treatment of GBS colonization is ineffective in eliminating carriage and does not prevent neonatal disease. 1
- Oral antibiotics may promote antibiotic resistance without providing adequate protection. 1
- Effective prophylaxis requires multiple intravenous doses continued until delivery, not a single oral dose. 1
Specific Treatment Protocol
Initial dosing:
- Penicillin G: 5 million units IV initially, then 2.5-3 million units IV every 4 hours until delivery. 1
- Ampicillin is an acceptable alternative: 2 g IV initially, then 1 g IV every 4 hours. 1
For penicillin-allergic patients:
- Low-risk allergy: Cefazolin 2 g IV initially, then 1 g IV every 8 hours. 1, 2
- High-risk allergy (anaphylaxis history): Clindamycin 900 mg IV every 8 hours or vancomycin 1 g IV every 12 hours. 1, 2
Critical Clinical Pitfalls to Avoid
- Do not delay obstetric interventions solely to provide 4 hours of antibiotic administration before birth. 3
- Even short durations of prophylaxis (as little as 2 hours) have been shown to reduce GBS vaginal colony counts and achieve fetal serum levels significantly above the minimal inhibitory concentration for GBS. 3, 4
- The CDC guidelines make no distinction between treated and untreated GBS-positive women—both require intrapartum prophylaxis. 1
- Never rely on antepartum oral antibiotics as a substitute for intrapartum IV prophylaxis, as this approach has been proven ineffective. 1