The GBS3 Trial

GBS is the most common cause of life-threatening infection in newborn babies in the UK.

Most developed countries offer all pregnant women a GBS test late in pregnancy and antibiotics in labour if the test result is positive. These countries have seen significant drops in the rates of GBS infection in newborn babies. Since 2003, the UK has used a risk-based approach to identify which newborn babies are most likely to develop GBS infection and to determine who to offer antibiotics in labour to reduce that risk to the baby. Our rate has risen.

What is the GBS3 Trial?

GBS3 is a major UK clinical trial investigating how best to prevent group B Strep (GBS) infections in newborn babies. GBS is the most common cause of life-threatening infection in newborns in the UK, and the trial aims to find out whether routine testing of pregnant women and people is more effective than the current risk-based approach.

Why is this Trial important?

Currently, the UK does not routinely offer all pregnant women and people testing for GBS. Instead, antibiotics are offered during labour only if certain risk factors are present. However, this approach has not reduced GBS infection rates in babies, and the UK lags behind other countries that do offer routine testing.

The GBS3 trial is designed to provide the evidence needed to decide whether the UK should change its national policy and start routinely testing pregnant and people for GBS.

How did the Trial work?

The trial involved 71 hospitals across England and Wales. These hospitals were randomly assigned to one of three groups:

• Standard care group: continued with the current UK risk-based strategy.
• ECM testing group: offered a lab-based test for GBS at 35–37 weeks of pregnancy.
• Rapid test group: offered a quick bedside test for GBS during labour.

All pregnant women and people giving birth at a participating hospital were cared for according to the hospital’s assigned strategy.

Who took part?

Around 320,000 pregnant women and people and their babies were involved in the trial. 71 hospitals participated in the GBS3 trial, listed below.

What happens next?

Recruitment for the trial ended on 31 March 2024, and the research team is now analysing the data. Results are expected to be published in 2026, and will help shape future GBS prevention policy in the UK. 

Papers published so far

Below are links to papers published so far about the GBS3 Trial:

Universal maternal testing for group B streptococcus in late pregnancy: process outcomes and alongside qualitative study for the GBS3 trial. Daniels JP, Walker KF, Bradshaw L, Dorling J, Ojha S, Gray J, Thornton JG, Plumb J, Petrou S, Ayers S, Mitchell E, Downe S, Grace N, Cooper T, Plachcinski R, Moore S, Jones AM, Harrison E, Brooks J, Barker-Williams K, Hollands H, McLeavey SK, Willson S, Webster S, Carpenter J, Hyslop Peart M, Wills L, Haines R, Haydock R, Sadiq S, Fiaschi L, Evans L, Ogollah R, Seale J, Spas S, Huang L, Moody S; GBS3 Collaborative Group. Early Hum Dev. 2025 Nov 17;213:106442. doi: 10.1016/j.earlhumdev.2025.106442. Epub ahead of print. PMID: 41325655.

Routine testing for group B streptococcus in pregnancy: protocol for a UK cluster randomised trial (GBS3). Daniels J, Walker K, Bradshaw L, Dorling J, Ojha S, Gray J, Thornton J, Plumb J, Petrou S, Madan J, Achana F, Ayers S, Constantinou G, Mitchell EJ, Downe S, Grace N, Plachcinski R, Cooper T, Moore S, Jones AM, Harrison E, Brooks J, Barker-Williams K, Hollands H, Mcleavey SK, Willson S, Webster S, Carpenter J, Hyslop-Peart M, Wills L, Haines R, Haydock R, Sadiq S, Fiaschi L, Evans L, Ogollah R, Seale J, Spas S, Huang L, Moody S, Abramson J; GBS 3 Collaborative Group. BMJ Open. 2025 Jun 17;15(6):e087887. doi: 10.1136/bmjopen-2024-087887. PMID: 40527563; PMCID: PMC12182030.

The acceptability of implementation of group B Streptococcus testing: Perspectives from women and health professionals in the GBS3 trial: A qualitative study. Constantinou G, Ayers S, Mitchell EJ, Walker KF, Downe S, Jones AM, Moore S, Daniels JP; GBS3 Collaborative Group. Women Birth. 2024 Nov;37(6):101832. doi: 10.1016/j.wombi.2024.101832. Epub 2024 Oct 16. PMID: 39418758.

The clinical and cost-effectiveness of testing for group B Streptococcus in pregnancy: a cluster randomised trial with economic and accessibility evaluations (GBS3). Final trial protocol. Published 13 December 2023.

GBSS’s role

Group B Strep Support (GBSS) has been closely involved in the GBS3 trial from the beginning. We’ve supported the trial team, helped raise awareness, provided the perspective of families, and provided updates to both families and healthcare professionals. We look forward to the results and hope they will lead to better protection for newborn babies across the UK.

For more information

There’s more information on the GBS3 Trial website here and on the NIHR website here. We will be sending people updates about the GBS3 Trial – sign up here – or get in touch with us at info@gbss.org.uk if you need any information.