Prevention of Early-Onset Group B Streptococcal Disease
Background
Group B Streptococcus (GBS, Streptococcus agalactiae) colonises the bowel and genital tract of 20–40% of adults. Carriage in pregnancy is usually asymptomatic and intermittent. GBS is the most common cause of severe early-onset infection (EOGBS, onset <7 days of age, most within 12–24 hours of birth) in newborn infants in the UK, with an incidence of roughly 0.57/1,000 births. Transmission is vertical, typically during labour or after rupture of membranes.
Risk-Factor-Based Approach vs Universal Screening (key exam point)
The UK does not offer universal bacteriological screening for GBS to all pregnant women. Instead, the UK operates a risk-factor-based strategy: intrapartum antibiotic prophylaxis (IAP) is offered to women with specific clinical risk factors or a positive incidental GBS result, rather than testing every woman antenatally. This contrasts with the USA/many other countries, which use universal culture-based screening at 35–37 weeks.
The UK National Screening Committee has repeatedly concluded that universal screening should not be introduced, because:
- Many women who carry GBS at one point in pregnancy will not be carrying it at delivery (intermittent/transient carriage), and vice versa — screening earlier in pregnancy poorly predicts colonisation status at birth
- A screen-and-treat programme would substantially increase antibiotic exposure in labour without clear proof of reducing neonatal mortality
- No trial evidence (until GBS3) directly compared universal screening against the risk-factor approach for clinical outcomes
- Routine antenatal culture swabbing for GBS is not recommended as part of standard antenatal care
Exam pitfall: candidates often assume the UK screens all women like the USA does — it does not. The guideline explicitly states GBS testing should not be offered as a matter of routine to all women.
Indications for Intrapartum Antibiotic Prophylaxis (IAP)
IAP should be offered to women with any of the following:
- GBS identified incidentally in the urine or on a vaginal/rectal swab during the current pregnancy
- A previous baby with early- or late-onset GBS disease
- GBS bacteriuria of any colony count detected during the current pregnancy
- Pyrexia in labour (temperature ≥38°C) — broad-spectrum antibiotics covering GBS should be given
- Preterm labour (regardless of GBS status, unless GBS has already been excluded)
- Prolonged rupture of membranes (≥18 hours) in a woman known to be, or at increased risk of being, GBS-colonised
Women who are found incidentally to have had GBS colonisation in a previous pregnancy (with no other risk factor in the current pregnancy) should be informed and offered the choice of IAP or testing (enriched culture medium) later in the current pregnancy — carriage does not necessarily persist between pregnancies.
Planned caesarean birth in the absence of labour and with intact membranes does not require GBS IAP, even in a colonised woman, because the main risk is exposure during labour/rupture of membranes.
Antibiotic Choice
- First-line: intravenous benzylpenicillin — loading dose, then repeated doses every 4 hours until birth. Give as soon as possible after onset of labour/decision for IAP.
- Penicillin allergy (non-severe): cefuroxime is used.
- Severe penicillin allergy: vancomycin.
- Clindamycin is no longer recommended as first-line for penicillin-allergic women due to high and rising rates of GBS resistance.
- IAP is most effective when the interval from first dose to birth is ≥4 hours.
Neonatal Monitoring
Management of the newborn depends on maternal risk factors and duration of IAP received, not on giving the baby prophylactic antibiotics as a default:
- Well babies whose mothers received adequate IAP (≥4 hours before birth) with no other concerns generally require only standard postnatal observations — routine antibiotics for the baby are not indicated.
- Babies of GBS-colonised/risk-factor mothers who did not receive adequate IAP (e.g., declined, or <4 hours before birth) should have regular clinical observations (vital signs, feeding, tone, colour) for at least the first 12 hours of life, with a lower threshold for extending observation or starting empirical antibiotics if there are any signs of possible infection.
- Babies showing clinical signs of possible early-onset infection (respiratory distress, temperature instability, poor feeding, lethargy, tachycardia) at any point should be promptly assessed and started on empirical antibiotics (e.g., benzylpenicillin and gentamicin) without waiting for culture results, per neonatal early-onset sepsis guidance (NICE NG195).
- Early discharge (<12 hours) is discouraged for babies at increased risk who have not completed a period of observation.
High-Yield Exam Points
- The UK uses a risk-factor-based approach, not universal antenatal culture-based screening — a classic distractor is describing 35–37 week universal screening as UK practice (that is the US/CDC model, not RCOG).
- Routine antenatal GBS swabbing is not part of standard UK antenatal care.
- Key IAP indications: current-pregnancy GBS on swab or urine (any colony count), previous baby with GBS disease, intrapartum pyrexia ≥38°C, preterm labour.
- First-line IAP is IV benzylpenicillin, given as early as possible and repeated until birth; clindamycin is not recommended due to resistance.
- IAP is most protective when given ≥4 hours before birth — this interval determines the intensity of neonatal observation, not a blanket rule of giving every baby antibiotics.
- Planned pre-labour caesarean with intact membranes does not require GBS IAP.
- Babies with clinical signs of infection are treated empirically without waiting for culture — management follows NICE NG195 for early-onset neonatal sepsis.
Source: RCOG Green-top Guideline No. 36 (3rd edition, September 2017 (Hughes et al., BJOG 124(12):e280–e305) — still the current edition; the UK National Screening Committee has said it will review its no-screening position once the GBS3 cluster-randomised trial (results expected 2026) reports)
Read the original on rcog.org.uk
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