Group B Streptococcus (GBS) is a bacterium that lives harmlessly in the gut and vagina of roughly one in five pregnant women. For the women who carry it, there are no symptoms and no treatment is needed during pregnancy itself. The concern arises around labour and delivery, because the bacterium can pass to the baby, and in a small number of cases it causes serious, rapidly progressing infection.
The disparity between how common carriage is and how serious the consequences can be creates understandable anxiety. Understanding the actual risk, who is most vulnerable, what the warning signs in a newborn look like, and what happens if GBS infection is suspected allows parents to respond usefully rather than anxiously.
Healthbooq (healthbooq.com) covers pregnancy, labour, and newborn health.
What Group B Streptococcus Is
GBS (Streptococcus agalactiae) is a gram-positive bacterium that colonises the digestive tract and genitourinary tract of adults without causing illness. It is not a sexually transmitted infection. Roughly 20-40% of adults carry it at any one time, and carriage comes and goes – a woman who tests positive at 37 weeks may test negative at 40 weeks and vice versa.
In newborns, the immune system is not yet capable of fighting off GBS if it enters the bloodstream. The bacterium can cause sepsis, pneumonia, or meningitis. Without rapid antibiotic treatment, these conditions progress quickly and can be fatal or cause permanent neurological damage.
GBS is the most common cause of serious bacterial infection in newborns in the UK, causing approximately 340 cases of early-onset disease annually, with around 25 deaths and around 50 cases of long-term disability, according to Group B Strep Support (GBSS).
Early-Onset Versus Late-Onset Disease
Early-onset GBS disease occurs within the first 6 days of life (most within 24 hours) and typically results from transmission during labour or delivery. It is the more common and more severe form.
Late-onset GBS disease occurs between 7 and 90 days of age and may or may not be related to maternal carriage. It has a higher rate of meningitis and a worse neurological outcome than early-onset disease.
The UK Approach: Risk-Based Rather Than Universal Screening
Many countries, including the United States, offer universal GBS swab testing at 35-37 weeks of pregnancy and give IV antibiotics in labour to all women who test positive. The UK does not currently follow this approach. The UK National Screening Committee reviewed the evidence in 2017 and again subsequently, and concluded that universal screening did not reduce early-onset GBS disease rates compared with risk-based management.
The reasons are partly technical: a swab taken at 35-37 weeks does not accurately predict who is carrying GBS at the time of delivery. Offering IV antibiotics to every woman who tests positive (perhaps 25-30% of pregnant women) would mean a very large number of women receiving antibiotics in labour, with consequences for maternal gut microbiome, increasing antibiotic resistance, and risk of anaphylaxis, while the additional benefit over risk-based care appears small in the evidence.
Private GBS testing is available (a low vaginal and rectal swab sent to a private laboratory), and some parents choose this for reassurance. A positive result would be shared with the midwifery team and would change management toward IV antibiotics in labour in many cases, though the NHS does not automatically offer antibiotics based solely on private testing results – this requires a conversation with the maternity team.
Risk Factors That Trigger IV Antibiotics in Labour
Current NICE guidance (NG195) recommends offering IV antibiotics during labour to women with any of the following:
A previous baby with GBS disease (the single strongest risk factor, justifying antibiotics regardless of current carriage status). GBS found incidentally in urine during this pregnancy (bacteriuria – a higher bacterial load than vaginal carriage). GBS identified on a swab during this pregnancy. Preterm labour before 37 weeks. Prolonged rupture of membranes (more than 18 hours before delivery). Fever in labour (38 degrees or above), which may indicate chorioamnionitis.
IV penicillin is the antibiotic of choice; women allergic to penicillin should tell their team so an alternative (cefazolin or clindamycin) can be arranged.
Signs of GBS Infection in a Newborn
Parents should know what to look for in the first days and weeks. GBS infection in newborns can look like general unwellness and deteriorate fast.
Warning signs include: breathing fast or with difficulty; grunting sounds when breathing; very pale or mottled skin; unusual limpness or floppy muscle tone; not feeding or not waking to feed; temperature above 38 degrees or below 36 degrees; seizures; a high-pitched, unusual cry.
Any newborn showing these features needs urgent assessment – call 999 or go to the nearest emergency department without waiting.
Treatment
GBS infection is treated with IV antibiotics (typically benzylpenicillin and gentamicin) in hospital. Treatment started early significantly improves outcomes. Delayed presentation – when parents wait to see if the baby improves – is a major factor in poor outcomes.
Key Takeaways
Group B Streptococcus (GBS) is the most common cause of life-threatening infection in newborns in the UK, causing meningitis, sepsis, and pneumonia. Around 20-40% of pregnant women carry GBS in the vagina or rectum as normal flora, with no symptoms. Most babies born to GBS-positive mothers remain well, but early-onset GBS disease (occurring within 6 days of birth) can develop very rapidly and be fatal without prompt treatment. The UK does not currently offer universal screening; the National Screening Committee has reviewed the evidence and concluded that universal screening does not improve outcomes compared with risk-based management. Knowing the risk factors and signs of GBS infection in newborns is important for all parents.
