About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- GBS colonises the vagina/rectum in ~20–30% of UK women. Most are asymptomatic
- UK does NOT routinely screen for GBS (risk-based approach, unlike USA which universally screens)
- Intrapartum antibiotic prophylaxis (IAP) offered if: previous GBS-affected baby, GBS detected in current pregnancy, preterm labour, PPROM ≥18 h, intrapartum fever ≥38°C
- IAP: IV benzylpenicillin 3 g loading dose then 1.5 g every 4 hours until delivery. Clindamycin if penicillin allergy
- Early-onset GBS sepsis (EOGBS): presents within 72 h of birth — pneumonia, septicaemia, meningitis
- Babies of GBS-positive mothers: observe for ≥12 hours after birth for signs of sepsis
Overview
Group B Streptococcus (GBS, Streptococcus agalactiae) is a commensal bacterium that colonises the gastrointestinal and genitourinary tracts of approximately 20–30% of women. In pregnancy, vertical transmission during labour can cause early-onset neonatal sepsis (EOGBS), which presents within the first 72 hours of life with pneumonia, septicaemia, or meningitis. EOGBS carries significant morbidity and mortality. The UK adopts a risk-factor-based approach to prevention (rather than universal screening), offering intrapartum antibiotic prophylaxis to women with identified risk factors.
Epidemiology
GBS is the most common cause of early-onset neonatal sepsis in the UK. The incidence of EOGBS in the UK is approximately 0.5 per 1,000 live births, with a case fatality rate of ~5–6%. GBS colonisation is transient and intermittent, meaning a positive swab earlier in pregnancy does not reliably predict colonisation at delivery. Risk factors for EOGBS include previous GBS-affected infant, preterm delivery (<37 weeks), prolonged rupture of membranes (≥18 h), and maternal intrapartum fever.
Clinical Features
Symptoms
Maternal GBS colonisation is asymptomatic
May be incidentally detected on vaginal or urine culture
GBS UTI/bacteriuria during pregnancy — a marker of heavy colonisation
Signs
No maternal signs from colonisation alone
Neonatal EOGBS: poor feeding, lethargy, temperature instability, respiratory distress, apnoea
Neonatal tachypnoea, grunting, cyanosis (GBS pneumonia)
Neonatal seizures, bulging fontanelle (GBS meningitis)
Investigations
First-line
Vaginal/rectal swab (enrichment culture)Gold standard for GBS detection. NOT routinely performed in the UK. Sensitivity >90% if taken at 35–37 weeks (USA protocol)
Urine cultureGBS bacteriuria in pregnancy indicates heavy colonisation — treat as per UTI AND offer IAP in labour
Second-line
Point-of-care rapid GBS test (PCR)Intrapartum PCR testing available in some units — results within 1 hour. Being evaluated for wider UK use
Specialist
Neonatal blood cultures and LPIf neonatal sepsis suspected — blood cultures, LP (CSF for MC&S), CRP, FBC
1
Intrapartum antibiotic prophylaxis (IAP) — indications
- Previous baby with invasive GBS disease
- GBS colonisation, bacteriuria, or infection detected in current pregnancy
- Preterm labour (<37 weeks)
- Prolonged rupture of membranes (≥18 hours at term)
- Intrapartum fever ≥38.0°C
2
IAP regimen
- IV benzylpenicillin 3 g loading dose, then 1.5 g every 4 hours until delivery
- If penicillin allergy (non-anaphylaxis): IV cephalosporin (e.g., cefuroxime)
- If penicillin allergy (anaphylaxis risk): IV clindamycin 900 mg every 8 hours (check local sensitivity data)
- IAP should ideally be given ≥4 hours before delivery for maximum efficacy
3
Neonatal management
- Well babies born to GBS-positive mothers receiving adequate IAP: observe for 12 hours
- Well babies with inadequate or no IAP: enhanced clinical observation for at least 12 hours
- Unwell babies or signs of sepsis: urgent blood cultures and empirical IV antibiotics (benzylpenicillin + gentamicin)
- Follow NICE NG195 (Neonatal infection) guidance for assessment and treatment
Complications
- Early-onset GBS disease: Pneumonia (~50%), septicaemia (~30%), meningitis (~10%). Case fatality ~5–6%
- Late-onset GBS disease: 7 days to 3 months — typically presents as meningitis. Not prevented by IAP
- Neonatal mortality and long-term disability: Survivors of GBS meningitis may have hearing loss, developmental delay
UKMLA Exam Tips
- 1UK uses risk-factor approach to GBS (NOT universal screening). This is a commonly tested fact
- 2IAP indications: previous affected baby, GBS in current pregnancy, preterm labour, PPROM ≥18 h, intrapartum fever
- 3IAP = IV benzylpenicillin (3 g then 1.5 g every 4 h). NOT oral antibiotics. NOT antenatal treatment
- 4GBS bacteriuria = heavy colonisation — treat UTI AND offer IAP in labour
- 5GBS is the commonest cause of early-onset neonatal sepsis in the UK
- 6IAP does NOT prevent late-onset GBS disease (>7 days)
practicetest your knowledge on group b streptococcus in pregnancyApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — obstetrics and beyond.
open q-bank