Group B Strep: What It means in pregnancy and how to lower your risk
What is Group B Strep?
Group B strep, sometimes known as GBS, is a type of bacteria called Streptococcus agalactiae. It is commonly found in the intestines, rectum and vagina of women at low numbers, and is normally quite harmless (most people won’t realise they have it).
At any one time, around 20 to 40% of women carry Group B strep.
Group B strep and pregnancy
Group B strep is something that gains attention in pregnancy, due to the rare chance it can spread to the baby during labour and cause an infection, such as sepsis, pneumonia, or meningitis, which can be very serious.
Approximately 1 in 1,600 of all babies born develops a Group B strep related infection. The likelihood of infection is higher in those carrying Group B strep; about 1 in every 400 babies born to women known to carry Group B strep develop a GBS related infection.
Most babies that come into contact with Group B Strep during labour or around birth will not become ill.
The stats on Group B strep in pregnancy:
On average, in the UK and the Republic of Ireland, every month:
- Around 70,000 live babies are born
- 66 babies are diagnosed with a Group B Strep infection
- 40 early-onset + 26 late-onset GBS infection
- of these, 56 babies make a full recovery
- 4 babies die from their Group B Strep infection
- 6 babies survive with long-term physical or mental disabilities
Any baby can develop a group B Strep infection, but the risk is higher in babies born preterm (before 37 weeks), in those with a sibling who previously developed a group B Strep infection, when a maternal fever or signs of infection are present during labour, when group B Strep has been detected during the pregnancy, and when more than 24 hours pass between waters breaking and labour starting.
How can mothers reduce the risk of Group B Strep colonisation in pregnancy?
Most NHS trusts do not test for Group B Strep during pregnancy, for various reasons: Group B Strep can be transient and so having it present 3 months before labour doesn’t necessarily mean it will be present during labour, testing isn't sensitive enough to detect all cases and so some are missed, and the down side of taking antibiotics may outweigh the benefits in some groups of low risk women.
However, we do appreciate some women will still be concerned about this microbe and may want to take some proactive steps to mitigating risks for their newborn.
Testing
We include streptococcus agalactiae in our vaginal microbiome test panel, for those wanting to check the health of their vaginal environment before labour. For any questions around taking this test and the best timing, please email: test@pelvicrelief.co.uk. This test is safe in pregnancy as its a low vaginal swab.
Oral lactobacillus probiotics
Secondly, oral lactobacillus (live bacteria) supplementation has been found in studies to reduce the likelihood of Group B strep colonisation in pregnant women. A 2022 study of women in their 3rd trimester showed the presence of lactobacilli in the vagina inversely correlated with Group B strep colonisation.
A healthy vaginal microbiome is found to be dominated by lactobacillus bacteria, and these work to prevent other opportunistic microbes, such as Group B Strep, candida, E.coli, and BV associated microbes, from taking up space and causing symptoms.
The lactobacillus bacteria in our probiotics formulation, Ultimate V, has been found to reach the vagina alive and acidify it; opportunistic microbes do not grow well in an acidic environment, so this clever mechanism is a really protective strategy against opportunistic microbes.
We recommend one capsule per day during pregnancy if needed, and this can be especially important in the run up to labour. Ultimate V is safe to take during pregnancy, but if you have any concerns alongside any existing diagnoses or medications, please check with your GP or email us at hello@pelvicrelief.co.uk.
Summary
In summary, newborn infections from Group B strep are relatively rare, however, the risk is increased with colonisation of this bacteria in the vagina and rectum.
One way to reduce the likelihood of Group B strep colonisation is to encourage lactobacillus dominance; this can be done by taking oral probiotic capsules containing lactobacillus strains found native to a healthy vagina.
References
Group B Strep Support. What is Group B Strep? Retrieved from https://gbss.org.uk/info-support/about-group-b-strep/what-is-group-b-strep/ (accessed December 2025).
Starc, M., Lučovnik, M., Eržen Vrlič, P., & Jeverica, S. (2022). Protective effect of Lactobacillus crispatus against vaginal colonization with Group B streptococci in the third trimester of pregnancy. Pathogens, 11(9), 980. https://doi.org/10.3390/pathogens11090980.
