Late Pregnancy · Labour
Group B Strep (GBS) — Testing & Antibiotics
GBS is a common bacterium (10-30% of women carry it) that can cause serious newborn infection if passed during labour. UK uses risk-based approach; US screens universally. Antibiotics in labour reduce risk by ~80%. RCOG Green-top 36 (2022).
Last reviewed 2 June 2026
GBS Intrapartum Prophylaxis
Which antibiotic and what dose?
Penicillin allergy
Recommended regimen
Penicillin G (first line)
Loading dose
5 million units IV
Maintenance
2.5–3 million units IV every 4 hours until delivery
Alternative: Ampicillin 2 g IV loading, then 1 g IV every 4 h.
Adequate prophylaxis = first dose of penicillin, ampicillin, or cefazolin ≥ 4 hours before delivery. Clindamycin and vancomycin are NOT counted as adequate by Kaiser EOS / AAP for newborn-side decisions (insufficient placental transfer data).
Educational tool only — not medical advice. ACOG CO 797 (2020 reaffirmed 2024) + CDC GBS 2024 + RCOG GTG 36. Indications for IAP: positive 36–37+6 wk vaginal/rectal screen, GBS bacteriuria this pregnancy, prior infant with GBS disease, OR unknown status + intrapartum risk factor (preterm < 37 wk, ROM ≥ 18 h, intrapartum temp ≥ 38 °C, or positive intrapartum NAAT). Decisions made by your obstetric team.
What does this mean?
Group B Streptococcus colonises 10–30 % of pregnant women, usually harmlessly. Without intrapartum antibiotic prophylaxis (IAP), about 1–2 % of babies born to colonised mothers develop early-onset GBS disease (sepsis, pneumonia, meningitis — case fatality ~5 %). Universal screening at 36+0–37+6 weeks plus IAP for positive carriers has reduced US early-onset GBS incidence from ~1.7 to ~0.25 per 1,000 births since the 1990s. The 4-hour rule matters because adequate placental transfer requires that interval — which is why penicillin / ampicillin / cefazolin given ≥ 4 h before delivery are counted as “adequate” in newborn EOS-risk calculators (Kaiser model), while clindamycin / vancomycin are not. Some UK units (RCOG GTG 36) favour a risk-based rather than universal- screening approach — both work if applied consistently.
What is GBS?
Group B Streptococcus is a BACTERIUM that lives in the vagina + rectum of 10-30% of healthy pregnant women — usually with NO SYMPTOMS.
Not an STI. Not poor hygiene. Just common gut/vaginal bacteria.
The concern: during labour, baby passes through birth canal and can pick up GBS. ~1-2% of babies born to GBS-positive mothers develop EARLY-ONSET GBS DISEASE (sepsis, pneumonia, meningitis). Intrapartum antibiotics reduce risk by ~80%.
How do I know if I have GBS?
- UK NHS: NO routine screening. Treats based on risk factors.
- US CDC: universal vaginal-rectal swab at 35-37 weeks.
- UK private: ECM (Enriched Culture Medium) test at 35-37 weeks (£35-75).
- Detected if GBS found in urine sample during pregnancy.
UK risk factors triggering antibiotics
RCOG Green-top 36 (2022) treats with IV antibiotics in labour if:
- Previous baby had GBS infection.
- GBS found in urine during current pregnancy.
- Preterm labour (<37 weeks).
- Prolonged rupture of membranes (>18-24 hours).
- Maternal fever in labour (≥38°C).
- Known positive swab in current pregnancy.
What antibiotics?
- Standard: benzylpenicillin (penicillin G) IV — 3g initial, 1.5g every 4 hours through labour.
- Penicillin allergy (mild): cefazolin 2g IV initial, 1g every 8h.
- Severe penicillin allergy: clindamycin (if GBS sensitive) or vancomycin.
- Effective within 2-4 hours.
- At least 4 hours before delivery for optimal protection.
Can I have a water birth with GBS?
Usually yes. GBS positive doesn’t exclude water birth automatically. IV cannula stays in arm; antibiotics given through it. Most UK units support this. Discuss in advance with midwife.
Water birth doesn’t increase GBS transmission to baby.
Does C-section avoid antibiotics?
- Planned elective C-section before labour AND before membranes rupture: NO antibiotics needed.
- Emergency C-section during labour or after membrane rupture: antibiotics STILL needed.
Signs of GBS infection in newborn
Early-onset (first week, often 24-48 hours):
- Grunting, fast breathing.
- Blue tinge.
- Floppy / lethargic.
- Fever or low temperature.
- Not feeding.
- Jaundice within first 24 hours.
Late-onset (1 week-3 months):
- Fever.
- Lethargic.
- Irritable.
- Feeding poorly.
- Seizures.
Any of these: seek urgent paediatric / NICU assessment.
Private testing — should I?
Personal choice. ECM (Enriched Culture Medium) test — most accurate — available privately UK (£35-75; at-home kit + lab).
Pros: peace of mind, easier birth planning. Cons: antibiotic downsides (allergic reactions ~10%, gut microbiome effects on baby), UK risk-based approach is evidence-based.
Different scenarios — GBS
Scenario 1: First pregnancy, no risk factors, UK NHS
Standard care, no testing, no antibiotics unless risk factors develop in labour. Most babies fine.
Scenario 2: GBS detected in urine at 28 weeks
Antibiotics in labour automatic regardless of later swabs. Cannula in early labour. Otherwise normal labour.
Scenario 3: Previous baby had GBS sepsis
Antibiotics in all subsequent pregnancies, regardless of swab results. May be discussed for elective C-section in extreme cases.
Scenario 4: Private testing positive at 36 weeks
Antibiotics in labour. Plan: arrive at unit in early labour; cannula; penicillin IV. Otherwise normal labour. Water birth still possible.
Scenario 5: Penicillin allergy, GBS positive
Cefazolin if mild allergy; clindamycin / vancomycin if severe anaphylaxis history. Discuss with anaesthetist + obstetric team antenatally.
Care guidance — GBS in pregnancy
- UK NHS: risk-based, no routine screening.
- Private ECM test at 35-37 weeks if you want.
- Tell midwife if previous GBS baby or GBS in urine this pregnancy.
- Antibiotics in labour if positive or risk factors.
- Cannula needed — doesn’t limit birth.
- Water birth usually still possible.
- Watch newborn for sepsis signs first 48 hours.
- Late-onset: vigilance through 3 months.
- Breastfeed as normal — helps gut flora.
- Recurrent GBS not your fault; just biology.
Sources
- RCOG Green-top Guideline 36 (2022). Prevention of Early-Onset Neonatal Group B Streptococcal Disease.
- NICE NG201. Antenatal care.
- CDC. Prevention of Group B Streptococcal Early-Onset Disease in Newborns. ACOG / CDC consensus.
- Group B Strep Support (UK charity). gbss.org.uk.
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Frequently asked questions
What is GBS?
Group B Streptococcus (Streptococcus agalactiae) is a BACTERIUM that lives in the vagina + rectum of 10-30% of healthy pregnant women — usually CAUSING NO SYMPTOMS. NOT a sexually transmitted infection. NOT poor hygiene. Just a common gut/vaginal bacteria. The CONCERN: during labour, baby passes through birth canal and can pick up GBS. ~1-2% of babies born to GBS-positive mothers develop EARLY-ONSET GBS DISEASE (sepsis, pneumonia, meningitis in first week of life). ~5% case-fatality if untreated. INTRAPARTUM ANTIBIOTICS during labour reduce risk by ~80%.
How do I know if I have GBS?
TWO COUNTRIES, TWO APPROACHES. UK NHS: NO ROUTINE SCREENING. Treats based on RISK FACTORS (see below). US (CDC since 1996): UNIVERSAL screening with VAGINAL-RECTAL SWAB at 35-37 weeks. If positive → antibiotics in labour. UK private screening (£35-75): can be done at 35-37 weeks. RAPID INTRAPARTUM TESTS (PCR) exist but not standard. CAN ALSO be detected if found in urine sample during pregnancy (then treated and considered colonised regardless of later swab).
Should I get private GBS testing in UK?
PERSONAL CHOICE. ARGUMENTS FOR: knowing your status, peace of mind, easier birth planning. ARGUMENTS AGAINST: small risk of disease in baby (~1-2 of every 1,000 babies); UK approach (risk-based) is evidence-based; antibiotics in labour have downsides (~10% allergic reaction, gut microbiome effects on baby, some yeast infection). UK STANDARD: risk factors include previous GBS baby, GBS in urine in current pregnancy, preterm labour (<37 wk), prolonged rupture of membranes (>18h), maternal fever in labour. PRIVATE TEST: ECM (Enriched Culture Medium) test — most accurate. Easy at-home kit + lab analysis.
What are the risk factors for treating without screening?
UK RCOG (Green-top 36, 2017 updated 2022) treats with antibiotics in labour IF: (1) PREVIOUS BABY had GBS infection; (2) GBS found in URINE during current pregnancy; (3) PRETERM LABOUR (<37 weeks); (4) PROLONGED RUPTURE OF MEMBRANES (>18-24 hours before birth); (5) MATERNAL FEVER in labour (≥38°C); (6) Known POSITIVE swab in current pregnancy. EVEN WITHOUT screening: these triggers catch most affected babies. UK approach criticised for missing some cases; US screening preferred by some advocacy groups.
What antibiotics are used?
STANDARD: BENZYLPENICILLIN (penicillin G) IV — 3g initial dose, then 1.5g every 4 hours through labour until delivery. EFFECTIVE within 2-4 hours. PENICILLIN ALLERGY (without anaphylaxis): cefazolin 2g IV initial, 1g every 8h. SEVERE PENICILLIN ALLERGY (anaphylaxis): clindamycin (if GBS sensitive) or vancomycin (if resistant). RECEIVED at least 4 HOURS before delivery for optimal protection. SHORTER COVERAGE still partially effective.
What if my baby is born before antibiotics work?
PARTIAL COVERAGE (any antibiotics) still helps. <4 HOURS coverage: baby observed more closely; pediatric/neonatal team review; blood tests / observation for 24-48 hours typical. STANDARD GBS positive + adequate antibiotics: usually 24-48 hour observation only. SHORT COVERAGE: more vigorous monitoring. ANY SIGN of infection in newborn (lethargic, fever, poor feeding, breathing difficulty): immediate sepsis workup + IV antibiotics.
Can I have a water birth with GBS?
YES — usually. GBS positive does NOT exclude water birth automatically. CONSIDERATIONS: (1) need to start IV antibiotics promptly — can be challenging in pool but possible (cannula remains in arm); (2) MOST UK MATERNITY UNITS support water birth with GBS positive if antibiotics started in time; (3) DISCUSS in advance with midwife. SOME UNITS more restrictive — check yours. WATER birth doesn't increase GBS transmission to baby.
Does C-section avoid the need for antibiotics?
DEPENDS. PLANNED ELECTIVE C-SECTION before labour AND before membranes rupture: NO antibiotics needed (baby doesn't pass through birth canal). EMERGENCY C-SECTION during labour or after membranes ruptured: ANTIBIOTICS still needed (baby may have been exposed). PRE-LABOUR planned C-section sometimes considered if very strong GBS concerns + other risk factors — uncommon, decision case-by-case.
Will GBS affect my baby long-term?
MOST babies born to GBS-positive mothers (~98-99%): UNAFFECTED. Those who develop early-onset GBS disease: ~70-80% recover fully with prompt treatment; ~5% mortality; long-term effects (especially after meningitis) include: developmental delay, hearing/vision problems, cerebral palsy in some survivors. LATE-ONSET GBS (1 week-3 months) less affected by intrapartum antibiotics — passed through breast milk or environment. EARLY DETECTION of newborn infection is critical.
What signs of GBS infection in newborn?
EARLY-ONSET (first week, usually first 24-48 hours): grunting, fast breathing, blue tinge, floppy / lethargic, fever or low temperature, not feeding, irritable, jaundice within first 24 hours. LATE-ONSET (1 week-3 months): fever, lethargic, irritable, feeding poorly, seizures, jaundice. ANY OF THESE: SEEK URGENT pediatric / NICU assessment. NOT NORMAL newborn behaviour — get seen.
Will I need IV cannula for antibiotics?
YES — antibiotics given IV (drip into vein). CANNULA stays in throughout labour. ALLOWS rapid additional dosing without re-cannulation. Can be inserted at admission. NOT particularly limiting — can still walk around, change positions, water birth possible, breastfeeding immediately. SLIGHT DISCOMFORT at insertion site; quickly forgotten in labour focus.
Can my partner have GBS too?
GBS is gut/vaginal bacteria. Partners may also carry; usually irrelevant. NOT an STI. NO TREATMENT of partner needed. NO CONCERN about future intimacy. Some women find GBS comes and goes between pregnancies — being positive once doesn't mean always positive. WHY SOME GET RECURRENT GBS: gut reservoir, individual flora. NOT YOUR FAULT — just biology.
What if I had GBS last pregnancy?
PREVIOUS BABY with GBS disease: antibiotics in labour for ALL subsequent pregnancies. PREVIOUS POSITIVE SWAB without baby affected: recommendations vary — some test again this pregnancy, some empirically treat. NHS GUIDANCE: treat with antibiotics if previous baby had GBS disease; otherwise test again. PRIVATE TESTING: 35-37 weeks current pregnancy for individual status. DISCUSS with midwife.
Are there alternatives to antibiotics in labour?
LIMITED EVIDENCE for alternatives. SOME STUDIES looked at chlorhexidine vaginal wash, probiotics, IV immunoglobulin — none consistently effective. UK / US GUIDELINES: antibiotics remain standard. PROBIOTICS during pregnancy MAY reduce GBS colonisation by birth — evidence weak; no harm trying (e.g. Lactobacillus rhamnosus GR-1 + reuteri RC-14 from Jarrow / similar). NOT a substitute for antibiotics if positive at term.
Will antibiotics affect my baby's gut?
SOME EFFECT possible. INTRAPARTUM antibiotics alter newborn gut microbiome temporarily — fewer beneficial bacteria initially. RECOVERS over weeks-months. EFFECTS controversial — possible slight increased risk of: asthma, eczema, antibiotic-resistant strains, jaundice. BREASTFEEDING helps restore gut flora. ANY EFFECT outweighed by benefit of GBS prevention. SOME parents give probiotics to baby — limited evidence; not harmful if done right.
How does this relate to other calculators on BumpBites?
Companion: /calculators/eos-sepsis for early-onset sepsis assessment; /calculators/bishop-score for labour readiness; /calculators/maternal-sepsis; /calculators/contraction-timer for labour onset; /calculators/birth-plan-builder for birth preferences; /calculators/hospital-bag-checklist.