Group B Streptococcus in Pregnancy
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Direct answer
Group B Streptococcus (Streptococcus agalactiae, a beta-haemolytic, Lancefield group B coccus) colonises the vagina and rectum of 10-30 per cent of pregnant women and causes early-onset neonatal sepsis — bacteraemia, pneumonia, and meningitis within the first week, usually within 24-48 hours of birth. Prevention is intrapartum antibiotic prophylaxis: penicillin G 5 million units intravenously, then 2.5-3 million units every four hours until delivery, given at least four hours before birth. Candidates are identified by universal rectovaginal culture at 36-37 weeks (ACOG/CDC) or by intrapartum risk factors — preterm labour, rupture 18 hours or more, fever, previous affected baby, GBS bacteriuria — the risk-based approach Indian practice largely follows.
What you must remember
- The organism: Streptococcus agalactiae, beta-haemolytic, Lancefield group B; capsular type III dominates late-onset meningitis; a commensal of the lower gut and genital tract.
- Disease split: early-onset (under 7 days, vertical transmission, presents as sepsis and pneumonia within 24-48 hours) versus late-onset (7-90 days, meningitis and bacteraemia, possibly transmitted postnatally — prophylaxis does not prevent it).
- Screening: rectovaginal swab (vaginal introitus then rectum, one swab) at 36-37 weeks, cultured in selective enrichment broth (Lim or Todd-Hewitt with nalidixic acid and colistin), reported with susceptibility for clindamycin in penicillin-allergic women.
- Indications for prophylaxis with unknown status: birth under 37 weeks, rupture 18 hours or more, intrapartum fever 38 degrees or more, GBS bacteriuria at any point this pregnancy, or a previous infant with invasive GBS disease.
- The regimen: penicillin G 5 million units IV loading, then 2.5-3 million units every 4 hours; penicillin allergy without anaphylaxis — cefazolin 2 g then 1 g 8-hourly; anaphylaxis — clindamycin 900 mg 8-hourly (if isolate susceptible) or vancomycin 1 g 12-hourly.
- Timing rule: antibiotics given at least four hours before delivery achieve adequate amniotic fluid levels; lesser intervals are recorded as inadequate prophylaxis.
- Not indications: colonisation in a previous pregnancy without current positive culture or bacteriuria, and caesarean with intact membranes and no labour.
Decision tree on the labour ward
A woman arrives at term, membranes ruptured 20 hours, no fever, unknown GBS status. The 18-hour rule fires: intrapartum prophylaxis is started — penicillin G 5 million units, then 2.5 million units four-hourly — while labour proceeds. Now vary the case. She reports a penicillin rash in childhood: no anaphylaxis, so cefazolin covers her safely. Had it been anaphylaxis with a documented colonising strain, the labour-ward slip would be checked for clindamycin susceptibility before choosing clindamycin over vancomycin. Suppose instead she carries a 36-week positive culture: prophylaxis at labour onset regardless of rupture duration. Suppose she had GBS urinary infection at 28 weeks: she was treated then, and she still receives intrapartum prophylaxis — bacteriuria counts as heavy colonisation. And a planned caesarean with intact membranes and no labour needs no GBS antibiotics, only routine surgical prophylaxis. The paediatric algorithm closes the tree: a well baby born after four or more hours of adequate prophylaxis needs observation only; a baby whose mother received inadequate or no prophylaxis is watched closely — and any symptomatic neonate gets blood cultures and empiric ampicillin-gentamicin, the Indian nursery standard.
The Indian position
India has not adopted universal antenatal GBS screening: culture logistics, cost, and reported colonisation rates lower than Western figures (Indian studies cluster between about 2 and 15 per cent) keep national practice risk-based, with intrapartum penicillin for the classic triggers — prolonged rupture, preterm labour, fever — and chorioamnionitis treated on its own merits. Tertiary centres are increasingly reporting early-onset GBS sepsis in their neonatal units, and reviews of Indian data have called for larger prevalence studies before deciding on screening policy — a genuinely debatable exam answer. Programme hooks worth quoting: neonatal sepsis management is standardised under the national sick newborn care units, and aseptic birth practices and early breastfeeding under Navjaat Shishu Suraksha Karyakram training indirectly reduce all early-onset sepsis. The viva trio: the drug (penicillin — erythromycin no longer acceptable due to resistance), the interval (at least four hours before birth), and the swab (rectovaginal at 36-37 weeks).
Frequently asked questions
When and how is GBS screening performed?
A single rectovaginal swab at 36-37 weeks, cultured in selective enrichment broth — the universal approach of ACOG/CDC; alternatives are intrapartum rapid tests or the risk-based strategy.
What is the intrapartum penicillin regimen?
Penicillin G 5 million units IV loading, then 2.5-3 million units every four hours until delivery — ideally starting at least four hours before birth.
Which women with unknown GBS status receive prophylaxis?
Those in preterm labour, with rupture 18 hours or more, intrapartum fever 38 degrees or above, GBS bacteriuria this pregnancy, or a previous infant with invasive GBS disease.
What is given to the penicillin-allergic woman in labour?
Cefazolin if allergy was not anaphylactic; with anaphylaxis, clindamycin 900 mg 8-hourly if the isolate is susceptible, else vancomycin 1 g 12-hourly.
Does intrapartum prophylaxis prevent late-onset GBS disease?
No — it targets vertical transmission in the first week; late-onset disease (7-90 days, often meningitis) is not prevented by intrapartum antibiotics.