GBS3 photo

The GBS3 Trial 



The trial completed recruitment on 31st March 2024. 

Thank you to all the midwives, doctors and many other hospital staff who helped to  make this trial happen.

And the biggest thank you to all the women, birthing people, partners and babies who were part of GBS3.


What is Group B Strep and the GBS3 Trial?

Group B Streptococcus is also known as GBS, Strep B or group B Strep. It is a common bacteria that normally causes no harm. In the UK, 1 in 4 pregnant women carry group B Strep in their vagina and rectum. You’re unlikely to know you carry it.

If you carry group B Strep, your baby may be exposed to it around labour and birth. While most babies won’t be affected, there is a very small chance of your baby becoming seriously ill or even dying. In extremely rare cases group B Strep infection can cause miscarriage, early labour or stillbirth.

This GBS3 trial is looking at whether testing pregnant women for Group B Streptococcus reduces the risk of infection in newborn babies compared to the current strategy in place in the UK. The current strategy in the UK is to offer antibiotics during labour to women who are considered at raised risk of their baby developing a group B Strep infection.

There are two different tests, which we are comparing against the current strategy. 

  • Lab Based Test at 3-5 weeks before anticipated delivery date (Enriched Culture Medium Testing)
  • Bedside Test at start of labour (Intrapartum Rapid Testing)


Key facts:

Why are we doing this trial?

The current UK strategy ‘risk factor screening’ is believed to be imperfect. Some babies are missed and develop group B Strep and some women with risk factors do not carry group B Strep. One possible solution is to test all women (universal screening) during pregnancy to determine if they carry group b Strep. However, in 2017, the UK National Screening Committee (NSC) concluded that they could not recommend universal screening for group B Strep in the UK. They suggested that a trial was undertaken to gather evidence on whether a universal screening program is both clinically and cost effective.



Who is involved in the trial?

71 hospitals are involved across England and Wales. Please go to the 'centres' part of this website for further information. See a map of the current hospitals involved.



My hospital is involved in the trial-what does this mean?

Each hospital involved in GBS3 trial is randomly allocated to one of 2 testing groups or will continue undertaking current strategy. 

This means that all women who are pregnant and give birth at that hospital will be treated in the same way (unless advised otherwise by your doctor or midwife).

Depending on what group your hospital has been assigned to will depend on whether you are tested for group B Strep and what type of testing you are offered.


There are two different tests, which we are comparing against the current strategy.


  • Lab Based Test at 3-5 weeks before anticipated delivery date (Enriched Culture Medium Testing)
  • Bedside Test at start of labour (Intrapartum Rapid Testing)


Please visit the 'testing groups' section of this website for more information. 


You will be asked to provide verbal consent prior to providing a swab (if your hospital has been allocated to one of the groups which requires a swab).


You will not need to provide written consent to be involved in this trial and your medical information will be collected from the hospital databases once you have given birth.


The study will use information routinely collected by the NHS about your labour and birth and your baby, which will all be linked together using your and your baby’s NHS/CHI numbers in a database kept by the Nottingham Clinical Trials Unit (NCTU).


This routine information will be anonymised once your information and your baby’s information has been linked and it will be deleted once the study has finished.


You may also be invited to take part in a telephone interview approximately 4-6 weeks after your baby (or babies) are born. If you are eligible and  interested in being involved in the telephone interviews, you will be given an additional information sheet with more information (for more information on the telephone interviews).



What happens if I don’t want to take part? 

If you are having your baby (or babies) in England, and you do not want your data to be used for this trial, you will need to contact the national data opt-out service.


This is a service that allows you to opt out of all your health information being used for all future research and planning, (not just for this study).


If you opt out of your data being used after it has been collected and processed, unfortunately it cannot be erased, as it will have already been anonymised.


For more information or to opt out of data collection go to:


If you are having your baby (or babies) in Wales, please speak to your Midwife, Doctor or GP about data opt out.


If you do not want a swab taken, you are free to decline, without giving any reason, and your care will not be affected in any way. Your routine data will still be used for study purposes.



How can I 'opt in' to having my health information used for research and planning if I have previously 'opted out?

If you have previoulsy 'opted out' of having all your health information used for all research and planning and you have changed your mind, then you will need to 'opt in'.


The process of 'opting in' is clearly set out on the 'Your NHS data matters' website.


If you 'opt in' then all your health information will be able to be used for all future research and planning including the GBS3 trial.


Who is running this trial?

The trial is being led by Professor Jane Daniels and Professor Kate Walker from the Nottingham Clinical Trials Unit (NCTU) at the University of Nottingham.


The trial is sponsored by the University of Nottingham.


The trial is being co-ordinated by the Nottingham Clinical Trials Unit at the University of Nottingham.


The trial is funded by the National Institute for Health Research’s Health Technology Assessment Programme (Project Reference 17/86/06).


This study is supported by Group B Strep Support (GBSS), and by the National Childbirth Trust (NCT).