Episode Summary: "GBS in Labor: Who Gets Antibiotics and Why"

Podcast: The OB/GYN Resident Survival Guide
Host: Dr. KC Miller
Episode: #20
Date: February 21, 2026

Episode Overview

This episode, hosted by Dr. KC Miller, offers a high-yield, clinically focused breakdown of Group B streptococcus (GBS) prophylaxis during labor. Aimed at OBGYN residents and medical students, it discusses which patients need intrapartum GBS antibiotics and reviews the rationale, evidence, and up-to-date regimens recommended by ACOG. The episode skillfully balances practical frameworks with details necessary for both the CREOG exam and everyday clinical decision-making.

Key Discussion Points & Insights

What is GBS and Why Does It Matter?

• GBS (Group B streptococcus) is a common part of the GI and vaginal microbiome.
  • "About 10 to 30% of pregnant patients will have colonization in the vagina and/or rectum, and of those... about 50% will transmit that bacteria to their newborns during labor or following membrane rupture." — Dr. Miller [02:04]
• If not prevented, transmission can cause early onset GBS disease in newborns (sepsis, pneumonia, or meningitis within 7 days).
  • "Even though that percent seems pretty low, this is actually the leading cause of neonatal sepsis in the early newborn period." — Dr. Miller [02:39]

Who Gets GBS Prophylaxis? (The "Who")

Dr. Miller clarifies two categories:

• Category 1: Known GBS Positive
  • Positive rectovaginal culture at/after 36 weeks, or GBS bacteriuria at any time in pregnancy
    • "GBS bacteriuria... suggests heavy rectovaginal colonization, which therefore increases the risk of GBS transmission to the neonate." [04:10]
• Category 2: GBS Status Unknown PLUS Risk Factors
  • Risk factors include:
    • Preterm labor (less than 37 weeks 0 days)
    • Prolonged rupture of membranes (≥18 hours)
    • Intrapartum maternal fever (≥38°C/100.4°F)
    • Prior GBS positivity in pregnancy
    • Prior infant with GBS early onset disease
    • Positive intrapartum nucleic acid amplification test (if available)
      • "However, if the test is negative but they're preterm or have any of the previously mentioned risk factors, prophylaxis should be administered anyway." [07:08]

GBS Prophylaxis Regimens (The "How")

• First-Line Antibiotics
  • IV Penicillin G: 5 million units loading, then 2.5–3 million units every 4 hours until delivery
  • IV Ampicillin: 2 grams loading, then 1 gram every 4 hours until delivery
    • "Regardless of the antibiotic being used, treatment should be initiated at least four hours before the anticipated delivery and continued until birth." [09:01]
• Penicillin Allergy Considerations
  • Determine severity (refer to ACOG table):
    • "A high risk penicillin allergy is defined as a prior reaction that presented with anaphylaxis, hives, a pruritic rash, angioedema, flushing, hypotension or respiratory distress..." [10:04]
  • Low-risk allergy: Use IV cefazolin (2 grams loading, 1 gram every 8 hours)
  • High-risk allergy:
    • If clindamycin-susceptible: Clindamycin 900mg IV every 8 hours
      • "It's really important... when you're placing the GBS culture order... that you enter into the order comments that the patient is pregnant and has a known penicillin allergy so that the lab is aware and can test the isolate for clindamycin resistance." [11:58]
    • If NOT susceptible or unknown: Vancomycin (weight-based IV dosing)

Clinical Pearls and Gray Areas

• Cesarean Delivery & GBS Prophylaxis:
  • GBS positive patients do NOT need prophylaxis for prelabor C-section if membranes are intact.
    • "The greatest predictor for transmission is membrane status, because if the membranes are intact, this provides a barrier between the lower genital tract and the amniotic cavity." [14:05]
  • For those in labor with intact membranes awaiting Cesarean, "Your attending may recommend initiating prophylaxis just in case because it's a bit of a gray area... but generally, so long as the membranes are intact, risk of transmission is low." [15:01]
• Validity of Negative GBS Cultures
  • Negative rectovaginal culture is valid for FIVE weeks from collection.
    • "If you have a patient that had a GBS culture result at 36 weeks and 0 days that somehow manages to stay pregnant beyond 40 weeks, it's important to repeat the rectovaginal culture to confirm that it is still negative." [16:05]

Notable Quotes & Memorable Moments

• The "Why" of GBS Protocol:

  • “The goal of intrapartum GBS prophylaxis is to reduce the risk of GBS early onset disease in the neonate.” — Dr. Miller [17:17]

• Practical Tip:

  • “If you're trying to figure out what dosing regimen to put your patients on, please refer to your own specific hospital protocol or reach out to your pharmacist as well as directly referencing the ACOG practice guidelines...” [09:44]

• Clinical Nuance:

  • “If the test is negative but they're preterm or have any of the previously mentioned risk factors, prophylaxis should be administered anyway.” [07:20]

Detailed Timeline of Important Segments

• [00:47] — Introduction to GBS, epidemiology, and neonatal risks
• [02:04] — Transmission statistics and early onset disease description
• [03:11] — Overview of who should receive intrapartum prophylaxis
• [04:10] — GBS colonization and bacteriuria explanations
• [05:37] — Risk factors for unknown GBS status
• [07:10] — The role of nucleic acid amplification testing in labor
• [09:01] — First-line antibiotic regimens and cautions
• [10:04] — Navigating penicillin allergies and severity assessment
• [11:58] — Clindamycin susceptibility testing and protocol
• [14:05] — Membrane status, cesarean section, and clinical gray zones
• [16:05] — Validity of negative cultures and repeat testing guidance
• [17:17] — Episode recap and high-yield summary

Key Takeaways

• GBS prophylaxis matters because it’s the primary intervention to prevent life-threatening early onset GBS disease in newborns.
• Know who to treat: Positive cultures, GBS bacteriuria, or unknown status with risk factors (preterm, prolonged rupture, fever, prior history)
• Antibiotic regimen: IV penicillin or ampicillin; use cefazolin, clindamycin, or vancomycin as per allergy assessment and culture sensitivity.
• Policy nuance: Membrane status is critical; prelabor cesarean with intact membranes generally does not need prophylaxis.
• Be vigilant: Negative cultures are valid for five weeks—repeat if gestation exceeds.

For further details or references, see ACOG Practice Bulletins and institutional protocols, as recommended by Dr. Miller.