Group B Streptococcus in Pregnancy
RCOG Green-top Guideline No. 36 Prevention of Early-onset Group B Streptococcal Disease. Last reviewed Sep 2017.
Scope and purpose of this article:
- Maternal risk assessment and preventive measures
- To reduce the risk of early-onset neonatal group B streptococcal disease (<7 days of age)
Background Information
Aetiology
Causative agent: group B beta-haemolytic streptococcus infection (Streptococcus agalactiae)
GBS colonisation (carriers) is present in the bowel & lower genital tract flora of 20-40% of adults.
Risk Factors
Risk factors that increase the chance of a baby developing early-onset group B streptococcal disease:
- Previous baby with GBS disease (50% chance in this pregnancy)
- Maternal GBS carriage during pregnancy (e.g. in urine, vagina, rectum)
- Preterm birth (<37 weeks)
- Prolonged rupture of membranes
- Suspected maternal intrapartum infection (e.g. chorioamnionitis)
- Maternal pyrexia during labour
Group B Streptococcal Disease in Newborns
GBS is the most frequent cause of severe early-onset infection in newborns (infants <7 days old).
Important red flags:
- Respiratory distress (starting >4 hours after birth)
- Seizures
- Signs of shock
- Need for mechanical ventilation in a term baby
Other clinical indicators:
- Abnormal behaviour
- Altered muscle tone (e.g. floppy)
- Difficulties with feeding
- Abnormal temperature (high or low)
- Tachypnoea, apnoea, hypoxia
- Jaundice within 24 hours of birth (pathological jaundice)
Diagnosis
Group B Streptococcus (GBS) Testing
The purpose of group B streptococcus testing is to detect pregnant womens that are colonised with group B streptococcus (carriers).
Universal screening should NOT be offered to all pregnant women
- The guideline explicitly stated that maternal request is NOT an indication for screening
- If the pregnant woman has a previous baby with GBS disease, IAP is automatically indicated without GBS testing
There are 2 ways and indications to detect GBS carriers (if indicated):
| Test | Test details | Indication | Subsequent action |
|---|---|---|---|
| Bacteriological testing | Method: separate vaginal and rectal swabs for culture
Timing: 35-37 weeks of gestation or 3-5 weeks prior anticipated delivery date |
GBS detected in a previous pregnancy (50% chance of being a carrier again) | Offer the choice of:
|
| Urine culture | Routine antenatal screening, or when investigating a suspected UTI | Depends on the findings:
In short, if GBS is detected in urine → IAP is necessary regardless |
|
Management (Group B Streptococcus Prophylaxis)
The mainstay to prevent neonatal early-onset group B streptococcal disease is maternal IAP (intrapartum antibiotic prophylaxis)
Indications for IAP
There are only 4 indications for IAP:
| Indications | Extra notes / description |
|---|---|
| Preterm labour | IAP should be offered regardless of GBS status and membrane status (intact or ruptured membranes)
Note that PPROM on its own is not an indication for IAP (erythromycin is given instead). It is the onset of preterm labour that necessitates IAP. |
| Previous baby with GBS disease | IAP should be offered automatically
Maternal bacteriological testing is NOT necessary |
| GBS carriage in current pregnancy | IAP should be offered if GBS is detected at any point during the current pregnancy, which includes:
|
| Intrapartum pyrexia (>38ºC) | Instead of routine IAP, RCOG recommends a broad-spectrum antibiotic regimen (e.g. IV amoxicillin or cefuroxime) that specifically includes coverage for GBS |
If a GBS +ve pregnant woman is undergoing a planned C-section with intact membranes and no signs of labour → GBS IAP is NOT required.
Vertical transmission of GBS and subsequent neonatal infection are highly unlikely in the absence of labour or ruptured membranes. Standard perioperative antibiotic prophylaxis for cesarean section should still be administered to reduce maternal postoperative infection risk, but this is not intended for GBS prophylaxis.
IAP Regimen
1st line: IV benzylpenicillin (Penicillin G)
- Timing to start IAP:
- Spontaneous labour → ASAP after the onset of labour or spontaneous rupture of membranes
- Induced labour → ASAP after established labour
- Once IAP has been given, it should be given regularly until the delivery of the baby
Be aware that the antibiotics are given to the mother, NOT to the newborn baby
Alternative antibiotics for penicillin allergy:
- Non-severe allergy → cephalosporin (e.g. IV cefuroxime)
- Severe allergy (e.g. anaphylaxis) → IV vancomycin
Women should be counselled that IAP reduces, but does NOT eliminate early-onset GBS disease (~80% effective).
As mentioned above, if IAP is indicated because of intrapartum pyrexia, RCOG recommends a broad-spectrum antibiotic regimen (e.g. IV amoxicillin or cefuroxime) instead of the above-mentioned antibiotics.
Patients with Pre-Labour Rupture of Membrane
The following applies to GBS +ve women:
| Scenario | Recommendation | |
|---|---|---|
| PROM at term (≥37 weeks) | Immediate induction of labour + IAP | |
| P-PROM (<37 weeks) | <34 weeks | Conservative management (premature risks outweigh GBS risks)
DO NOT induce labour immediately |
| 34-37 weeks | Immediate induction of labour may be beneficial
|
|
Also see the Preterm Labour and PPROM and PROM article.