# Group B Streptococcus in Pregnancy > Group B streptococcus in pregnancy notes for NEET-PG Obstetrics and Gynaecology: screening at 36 weeks, intrapartum penicillin prophylaxis doses. - Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/group-b-streptococcus-in-pregnancy - Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Group B Streptococcus in Pregnancy", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/group-b-streptococcus-in-pregnancy ## 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.