Labor Lensby LlaMamma

Group B Strep (GBS) in Pregnancy

A common bacteria that lives in the vagina or rectum of about 1 in 4 people; if present at birth it can rarely make a newborn sick, so IV antibiotics in labor are usually offered.

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What it is

Group B Streptococcus (GBS) is a normal bacteria that comes and goes in the body. It is not a sexually transmitted infection. In the U.S., pregnant people are typically screened with a vaginal-rectal swab around 36–37 weeks. If positive (or if certain risk factors are present without a swab), IV antibiotics — usually penicillin — are offered in labor to lower the chance the baby is exposed at birth. Without antibiotics, roughly 1–2 in 100 babies born to GBS-positive parents develop early-onset GBS disease; with antibiotics in labor, that risk drops substantially.

Evidence review links

Each link opens the full review on the publisher's site in a new tab.

Possible benefits

  • IV antibiotics in labor reduce early-onset newborn GBS infection by roughly 80%+[ACOG↗][CDC↗]
  • Screening is a simple swab; you can do it yourself in many clinics[ACOG↗]
  • Knowing your status lets you plan (timing of arrival, water breaking, birth location)[Evidence Based Birth↗]

Possible risks

  • Allergic reaction to antibiotics (usually mild; severe reactions are rare)[ACOG↗]
  • Possible short-term shifts in the newborn's gut bacteria; long-term effects are still being studied[Evidence Based Birth↗]
  • Requires an IV or heparin lock and being in the birth setting long enough for at least one dose (ideally ≥4 hours before birth)[ACOG↗]
  • Screening can miss people whose status changes between the swab and labor[Evidence Based Birth↗]

Alternatives

  • Risk-based approach (no swab; treat only if fever, preterm, prolonged rupture, or prior GBS baby) — less common in the U.S.[Evidence Based Birth↗]
  • Alternative antibiotics if you're allergic to penicillin — ask which one and why[ACOG↗]
  • Some parents decline antibiotics and plan close newborn observation; discuss the specific numbers with your care team[Evidence Based Birth↗]
  • Research on chlorhexidine vaginal wash exists but is not currently recommended as a substitute in most U.S. guidelines[Evidence Based Birth↗]
Run BRAIN with Labor LensGet Benefits, Risks, Alternatives, Intuition, and Nothing/Wait for Group B Strep (GBS) in Pregnancy — plus questions for your care team.

Current evidence

ACOG Committee Opinion 782 and the CDC recommend universal screening at 36 0/7–37 6/7 weeks and IV antibiotic prophylaxis in labor for positive results, unplanned cesarean before labor being an exception. Evidence Based Birth's GBS article summarizes the trade-offs, the size of the newborn benefit, and open questions about the infant microbiome.

Where the evidence is clear · where people may choose differently

For most topics, guidelines from ACOG, WHO, and other major bodies broadly agree on the core safety points (when to act in an emergency, informed-consent standards, monitoring baselines). Where reasonable people — and even guidelines — differ tends to be around thresholds (when to start or stop something), preferences (comfort, environment, support), and values (how you weigh small risks against benefits). Use the questions below to explore those pieces with your care team.

Educational only. Your care team can help you weigh what applies to your specific situation.

Questions to ask your care team

  • ?When and how will I be swabbed, and when will I get the results?
  • ?If I'm positive, which antibiotic will you use and how long before birth do you aim for the first dose?
  • ?What happens if labor moves faster than the 4-hour window?
  • ?If I'm allergic to penicillin, what will you use instead?
  • ?How will my baby be watched for signs of infection after birth?

Universal questions (works for any decision)

A short BRAIN-style set you can bring to any conversation about interventions, monitoring, or care decisions.

  • ?Why are you recommending this now — is it urgent, routine, or optional?
  • ?What happens if we wait an hour (or longer) before deciding?
  • ?What signs would tell us this is working — or that we need to change course?
  • ?What are the alternatives, including doing nothing?
  • ?What would you recommend if this were your family?
  • ?What would change your recommendation?

Sources & provenance

Tap a source to open the original guideline or review in a new tab.

Written in plain language from general guidance published by the listed organizations. No verbatim excerpts; editors should re-verify wording and numbers against the current source versions before publish.

Last reviewed: 2026-07-03

Further reading — canonical references

Read the source material directly. Each link opens the publisher's own current guidance in a new tab — cross-check what we summarize against what they say.

Educational only. Guidelines evolve — the linked publisher pages will reflect newer guidance than any static snapshot.

Version history — v1.0.0

  • v1.0.0 · 2026-07-03 · LlaMamma editors

    Initial GBS topic added with ACOG, CDC, and Evidence Based Birth references.

New guidance from ACOG, WHO, Evidence Based Birth, or other listed sources is recorded here and can be updated remotely without a new app release.