What group B strep is

The NHS describes it as "a type of bacteria called streptococcal bacteria" that "usually lives in the bottom (rectum) or vagina", is "normally harmless" and generally goes unnoticed. RCOG puts numbers on it: GBS "is carried in the vagina and rectum of 2–4 in 10 women (20–40%) in the UK", is not a sexually transmitted infection, and causes no symptoms in most carriers.

The concern is a narrow one. RCOG: "Around 1 in every 1750 newborn babies in the UK and Ireland is diagnosed with early-onset GBS infection." The NHS gives the same rate, describing the chance of it spreading to your baby during labour as happening "in about 1 in 1,750 pregnancies."

Most affected babies recover. RCOG's figures: "of the babies who develop early-onset GBS infection, 1 in 19 (5.2%) will die and, of the survivors, 1 in 14 (7.4%) will have a long-term disability."

Why the UK does not screen everyone

The NHS states that "routine testing is not currently recommended and tests are rarely done on the NHS. This is because group B strep is very common and testing cannot predict whether a baby will get an infection."

RCOG lists the UK National Screening Committee's fuller reasoning: most carriers' babies are born safely; screening late in pregnancy cannot accurately predict which babies will become infected; no test is entirely accurate and a negative swab does not guarantee you are not a carrier; many severely affected babies are born preterm, before the 35 to 37 week screening window; and universal treatment would mean "a very large number of women would receive treatment they do not need."

GBS is usually found incidentally — the NHS notes it "may be found during tests carried out for another reason, such as a urine test or vaginal swab." You can pay for a test privately.

Who is offered antibiotics in labour

NICE's neonatal infection guideline (NG195) gives the definitive list. Offer antibiotics during labour to people who:

are in pre-term labour, or
have GBS colonisation, bacteriuria or infection during the current pregnancy, or
had GBS colonisation, bacteriuria or infection in a previous pregnancy and have not since had a negative test by enrichment culture or PCR on rectovaginal swabs taken between 35 and 37 weeks or 3 to 5 weeks before the anticipated delivery date, or
have had a previous baby with an invasive GBS infection, or
have a clinical diagnosis of chorioamnionitis.

RCOG adds the practical cases: GBS found in your urine should be treated with antibiotic tablets straight away and you should be offered intravenous antibiotics in labour. If your waters break after 37 weeks and you are known to carry GBS, "you will be offered induction of labour straight away ... to reduce the time that your baby is exposed to GBS before birth."

Treating carriage before labour does not help. RCOG: "If you are found to carry GBS in your vagina or rectum, treating you with antibiotics before your labour begins does not reduce the chance of your baby developing GBS infection."

How much difference the antibiotics make

This is the number worth carrying into the conversation. RCOG: "These antibiotics reduce the risk of your baby developing a GBS infection in their first week of life from around 1 in 400 to 1 in 4000."

The NHS says the same in plainer terms — intravenous antibiotics during labour "can significantly reduce the risk of your baby getting ill."

The drug, and the timing

NICE specifies benzylpenicillin sodium for people without chorioamnionitis and no penicillin allergy. For a non-severe penicillin allergy, a cephalosporin with activity against GBS such as cefotaxime, used with caution. For severe penicillin allergy, vancomycin or an alternative guided by sensitivity testing or local surveillance data. Where chorioamnionitis is present, the regimens broaden to include gentamicin and metronidazole. RCOG confirms "the antibiotic that you will be offered ... is usually penicillin."

Timing is the whole point. NICE: "Give the first dose of antibiotics as soon as possible after labour starts (or as soon as infection is suspected, in the case of chorioamnionitis), and continue until the birth of the baby." RCOG describes the regimen as given "through a drip and continued at regular intervals (usually 4-hourly) until your baby is born."

Which is why both sources tell you to ring early. The NHS advises contacting your midwife "as soon as you go into labour or your waters break". RCOG: "it is important that you have antibiotics as soon as possible."

What it means for where you give birth

RCOG asks you to discuss planned place of birth in advance "to make sure that you can receive antibiotics as required in labour", noting that "if you choose to have antibiotics, they will be given through a drip and it may not always be possible to arrange this at home or in some midwifery-led units." The NHS similarly says your midwife "may recommend giving birth in hospital."

A drip does not have to mean lying still. RCOG: "You should still be able to move around freely during labour and this should not stop you from having a water birth."

One exception often missed: if you are having a planned caesarean and carry GBS, RCOG says "you do not need antibiotics to prevent GBS infection in your baby unless labour has started or your waters have broken." All women having a caesarean are offered antibiotics at the operation anyway, for different reasons.

The four-hour rule after birth

RCOG sets out how your baby is watched afterwards, and it turns on one threshold. "If your baby is born at full term (after 37 completed weeks) and you received antibiotics through a drip in labour at least 4 hours before giving birth then your baby does not need special monitoring after birth."

If your baby is at higher risk and you did not get antibiotics at least four hours before the birth, "your baby will be monitored closely for signs of infection for at least 12 hours", including general wellbeing, heart rate, temperature, breathing and feeding. If you have previously had a baby affected by GBS, monitoring for 12 hours happens regardless. After 12 hours, RCOG says the chance of infection is very low.

If you decline antibiotics, RCOG says "your baby will be monitored closely for 12 hours after birth as they are at increased risk".

What raises the risk, and what to watch for

RCOG lists the factors that make infection more likely: preterm birth, with earlier birth carrying greater risk; a previous baby affected by GBS; a high temperature or other signs of infection in labour; any positive urine or swab test in this pregnancy; and waters broken more than 24 hours before birth.

Most affected babies become unwell quickly — RCOG says "usually within 12–24 hours of birth". The NHS asks you to call 999 or go to A&E if your baby has symptoms of GBS infection, which include being floppy or unresponsive, grunting or working hard to breathe, very fast or slow breathing, an unusually high or low temperature, changes in skin colour or blotchy skin, not feeding well or vomiting milk up, and an unusually fast or slow heart rate. Symptoms can occasionally develop up to three months after birth.

Breastfeeding is safe. RCOG: it "has not been shown to increase the risk of GBS infection, and it offers many benefits to both you and your baby."

Group B Strep in Labour