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Group B streptococcus and intrapartum infection
Prevention of neonatal GBS disease rests on antibiotics for the mother during labour, at least 4 hours before birth, for every woman at risk; intra-amniotic infection is treated with broad antibiotics and delivery, and is not by itself a reason for caesarean section.
Why it matters in the exam
GBS questions test the indications for prophylaxis: a positive vaginal-rectal culture at 36–37+6 weeks, GBS in the urine at any stage of pregnancy, a previous infant with GBS disease, or unknown status with one of the risk factors — birth before 37 weeks, ruptured membranes for 18 hours or more, or a temperature of 38 degrees or more. The favourite question is when treatment is not needed: a planned caesarean before labour with intact membranes, even if the culture is positive. The antibiotic is asked too: penicillin is the choice, and with allergy — according to the severity of the allergy.
The second part is intra-amniotic infection (Triple I): maternal fever with fetal tachycardia, a high white count or purulent discharge. Treatment is IV ampicillin and gentamicin, antipyretics and progress to delivery; after caesarean section anaerobic cover is added (clindamycin or metronidazole). Intra-amniotic infection is not an indication for caesarean — labour continues in the usual way. The newborn of a mother with infection is evaluated for early-onset sepsis. Important: GBS bacteriuria in pregnancy is treated during pregnancy and also requires intrapartum prophylaxis without the need for a further culture.
Key points
- GBS culture at 36 to 37+6 weeks.
- Prophylaxis: positive culture, GBS bacteriuria, previous affected infant, or unknown status with a risk factor.
- Penicillin, at least 4 hours before birth.
- Intra-amniotic infection: ampicillin and gentamicin; not a reason for caesarean.
- Planned caesarean with intact membranes → no prophylaxis needed.
Summary table
| Situation | Definition or indication | Treatment | Exam notes |
|---|---|---|---|
| Screening | Vaginal-rectal culture at 36 to 37+6 weeks | — | Result valid for 5 weeks |
| Intrapartum prophylaxis | Positive culture, GBS bacteriuria, previous affected infant, or unknown status with a risk factor | IV penicillin G until delivery; alternative: ampicillin | Adequate if given at least 4 hours before birth |
| Penicillin allergy | Low risk of anaphylaxis | IV cefazolin | At high risk: clindamycin if the organism is susceptible, otherwise vancomycin |
| No prophylaxis needed | Planned caesarean before labour with intact membranes | — | Even if the culture is positive |
| Intra-amniotic infection | Fever 39 or more, or 38–38.9 repeated with fetal tachycardia, white count above 15,000 or purulent discharge | Ampicillin and gentamicin; after caesarean add anaerobic cover | Not an indication for caesarean |
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Sources
- ACOG Committee Opinion No. 797, 2020 — Prevention of Group B Streptococcal Early-Onset Disease in Newborns
- ACOG Committee Opinion No. 712, 2017 — Intrapartum Management of Intraamniotic Infection
- AAP Clinical Report, 2019 — Management of Infants at Risk for Group B Streptococcal Disease
- Williams Obstetrics, 26th edition (2022) — Maternal Infections
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.