Medical negligence

Group B Streptococcus Testing - What’s involved?

If you are a carrier of Group B Streptococcus (GBS), you usually have no symptoms, so testing is the only way to find out if you have GBS.

02 January 2024

If you are a carrier of Group B Streptococcus (GBS), you usually have no symptoms, so testing is the only way to find out if you have GBS. Carrying the bacteria is not harmful to the mother and it was previously believed that there was a small chance (1 in 1750) that it can affect your baby around the time of birth. GBS is the most common cause of infection in newborn babies causing meningitis, sepsis and pneumonia.

However recent research has highlighted that babies are 10 times more at risk from GBS than previously thought. A study by the University of Cambridge and Cambridge University Hospitals NHS Foundation Trust has found that 1 in 200 newborns are admitted to neonatal units with sepsis caused by GBS.

The NHS currently do not routinely test all pregnant woman for GBS. A test can however be done privately and this is quite simple, safe and effective.

What tests are available?

The two tests commonly used within the NHS to detect GBS are:

1. High Vaginal Swab Test (HVS) – standard ‘non-selective’ swab test

Procedure: Samples are taken usually from high up in the vagina, using a swab which looks like a long cotton bud. These are then processed in a lab. The result usually take two to five days to be confirmed.

The points to note about this type of test are as follows:

  • General-purpose but not specific to isolate GBS.
  • Not specifically designed to detect GBS and though it will detect GBS sometimes, this is often missed.
  • Positive result is highly reliable but a negative result is not so reliable as this test only finds GBS about half of the time that it is present.
  • So a positive HVS test can be trusted, but be wary of a negative HVS result.

2. Enriched Culture Medium Test (ECM) - GBS specific swab test

Procedure: Samples are taken from both the low vagina and rectum using one or more swabs and then processed in a lab.

The points to note about this test are as follows:

  • Specific to GBS detection and recommended by the Royal College of Gynaecology (RCOG) for women who carried GBS in previous pregnancy.
  • Recognised internationally as the ‘Gold Standard’ test to use when detecting GBS.
  • When properly performed within 5 weeks prior to delivery, a negative result is 96% predictive that a woman would not be carrying GBS at delivery and a positive result is 87% predictive that a woman would be carrying GBS at delivery.
  • Also recommended by Group B Streptococcus Support (GBSS).

3. Other Tests for GBS used during pregnancy

  • Urine tests: GBS may be found in a urine sample however a negative urine test only means that GBS has not been found in the urine. It is still likely that GBS is present in the vagina or rectum which is where the majority of GBS bacteria is found.
  • Rapid or bedside tests: A major UK research trial is underway looking at whether a rapid test is a good way of determining who to offer intravenous antibiotics in labour to, in order to prevent GBS infection in newborn babies. The results of the trial are due in the summer of 2025.

More information on the different tests for GBS can be found on the GBSS website.

When is it indicated/what would trigger the NHS to carry out a test in pregnancy?

The RCOG have summarised the key recommendations in their September 2017 Guidelines for prevention of early onset GBS. These are set out below:

  • If a woman carried GBS in a previous pregnancy and the baby did not develop GBS infection, an ECM test should be offered at 35-37 weeks (or earlier if preterm delivery is anticipated).
  • However feedback suggests that not all NHS hospitals offer to test for GBS and even if they do so, many maternity units still use a standard HVS test that misses up to half of the women carrying GBS.
  • The GBSS website advises that if you are offered a GBS test on the NHS it is very important to find out which test they are using, as not all tests are equally reliable.
  • In January 2018, a patient leaflet co-written by the RCOG and GBSS, was published and copies are available free of charge to families and the NHS.

Only a small group of woman, those who carried GBS in their previous pregnancy will be offered a GBS test through the NHS. Therefore it is recommended that women who want to test for GBS, arrange this through a private supplier.

Private testing – what is involved, process, costs and results

One of the easiest ways to test for GBS is to order a DIY testing kit.

  • Collecting the required swab samples is straightforward and the kits come with comprehensive and visual guides.
  • It is advisable to send the swabs to the laboratory between Monday and Thursday, so they’re not sitting in the postal system longer than necessary as samples deteriorate over time.

GBSS has partnered with selected companies which sell GBS kits privately. GBSS has a strict criteria that private GBS testing providers must meet with the charity, before being promoted on their website. The chosen companies provide only ECM tests which are internationally recognised as the ‘Gold Standard’ test for GBS carriage.

The GBSS trusted providers are as follows:

  • The Doctors Laboratory: This is GBSS' preferred provider of GBS testing and they have been providing ECM testing for over 20 years. The test costs around £37.50 and results are provided normally within 3-5 working days to your healthcare provider. A test can be ordered by clicking here.
  • Group B Strep Test: This is also recommended by GBSS. They use the Doctors Laboratory services (above) so their service is similar. A test can be ordered by clicking here.

It is crucial that the NHS offers to test pregnant women for GBS. Especially with the new findings confirming that newborns are up to 10 times more at risk from the GBS than previously thought. Preventative treatment, testing and data collection is urgently required within the UK.

The NHS should now more than ever, strongly follow the recommended clinical guidelines by the RCOG, that all pregnant woman should be offered an ECM test for free.

Group B Strep Support have excellent information leaflets for clinicians and patients that are used at several NHS Trusts and their campaigning has ensured that the latest Core Competency Framework for all NHS maternity healthcare professionals specifically includes training on GBS prevention and treatment. Group B Strep Support helpline no: 0330 120 0796 or email at

How can we help?

If you or your baby has been affected by group B strep infection and you believe the care/treatment you received from your medical professionals may have been substandard, please contact Laura Preston on

Laura is a Principal Lawyer and a medical negligence expert with a special interest in GBS cases and sits on the GBSS legal expert panel and is on hand to offer you expert legal advice.

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