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What is it
Group B Streptococcus (GBS) is a common vaginal/rectal bacterium. Most babies exposed during birth are fine, but a small number develop early-onset GBS infection (sepsis, pneumonia, meningitis) in the first week, which can be serious. Standard care in the US is a vaginal/rectal swab around 36–37 weeks; if positive, IV antibiotics (usually penicillin) are given during labor, ideally at least 4 hours before birth.
How your body works here
GBS lives harmlessly in about 1 in 4 pregnant people's vaginal/rectal tract. During labor it can travel up to the baby, especially after membranes rupture. IV antibiotics take about 4 hours to reach protective levels in the baby's blood via the placenta, killing bacteria before they can colonize the baby's lungs or bloodstream. That's why timing (dose given ≥4 hours before birth) matters as much as the antibiotic itself.
Benefits (B)
- Reduces early-onset GBS disease in newborns by roughly 80%.Review sources ↓
- Well-studied, inexpensive, and widely available.Review sources ↓
- Allows planned vaginal birth without extra newborn interventions in most cases.Review sources ↓
Risks (R)
- Allergic reaction (usually mild; severe anaphylaxis is rare — tell your team about any penicillin allergy so they can pick a safe alternative).Review sources ↓
- IV placement and being tethered to a pole for the infusion.Review sources ↓
- Antibiotic exposure may affect the baby's early gut microbiome; longer-term significance is still being studied.Review sources ↓
- Does not prevent late-onset GBS disease.Review sources ↓
Alternatives (A)
- Risk-based approach (used in some countries): antibiotics only if specific labor risk factors are present, rather than universal screening.Review sources ↓
- For a scheduled cesarean before labor with intact membranes, GBS antibiotics are generally not needed.Review sources ↓
- Decline (associated with a higher rate of early-onset GBS disease; discuss the specific plan for observing baby after birth if you decline).Review sources ↓
Evidence summary
ACOG (Committee Opinion 782) and CDC recommend universal 36–37 week screening and intrapartum antibiotics for GBS-positive people, PROM, prior GBS-affected baby, or GBS bacteriuria. This has cut early-onset GBS disease sharply since the 1990s.
Sources
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Questions to ask your provider
- What antibiotic will you use, and what's the alternative if I'm allergic?
- How does the timing work if my labor is fast?
- If I decline, how will you monitor the baby after birth?
- Does this change anything about my plan for movement, water, or eating in labor?
Intuition & Nothing/Wait (the I and N in BRAIN)
What is your gut telling you? What happens if you do nothing or wait?
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