Group B Strep: When Is It Tested?
Group B streptococcus (GBS) is a bacteria that many people carry without knowing it. In pregnancy, it becomes important because it can occasionally pass to a baby during birth and cause a serious infection. Understanding when and how it is tested — and what happens if you carry it — helps you make informed decisions with your midwife.
What Is Group B Strep?
Group B strep is a type of bacteria commonly found in the digestive system and vagina. Carrying it is not an illness — you will not have any symptoms — and it is harmless to healthy adults. In the UK, a significant proportion of pregnant women carry GBS at any given time, though carriage can come and go.
The concern in pregnancy is that a baby can pick up GBS bacteria while passing through the birth canal. Most babies exposed to GBS are completely unaffected, but in a small number of cases GBS can cause serious infections including sepsis, pneumonia, or meningitis in newborns. Prompt treatment with antibiotics during labour greatly reduces that risk.
Does the NHS Routinely Test for GBS?
No. The NHS in England, Scotland, Wales, and Northern Ireland does not offer routine GBS screening to all pregnant women. This is because routine screening would pick up many women who carry GBS at the time of testing but may not carry it at the time of birth (carriage can change), and the costs and risks of giving antibiotics to very large numbers of labouring women are weighed against a relatively small number of affected babies.
If you want to know your GBS status, you have two main options:
- Private GBS testing: You can arrange a private enriched culture medium (ECM) swab test, which is more sensitive than a standard swab. This is usually done between 35 and 37 weeks of pregnancy, when results are most predictive of your status at delivery. Several UK laboratories offer this test; your GP or midwife may be able to advise on local options, or you can arrange it directly.
- Incidental finding on another test: GBS is sometimes detected on a routine vaginal or urine swab taken for other reasons. If this happens, your midwife will discuss it with you.
Who Is Offered Antibiotics in Labour?
Even without routine screening, the NHS does offer intravenous antibiotics during labour to women at higher risk of passing GBS to their baby. This includes women who:
- Have previously had a baby affected by GBS infection
- Have tested positive for GBS in this pregnancy (on any swab or urine test)
- Go into labour before 37 weeks
- Have a temperature during labour (which can indicate infection)
- Have their waters break for an extended period before labour begins
If you carry GBS and are offered antibiotics in labour, they are given through a drip (IV) to ensure they work quickly. Oral antibiotics are not effective in this situation.
What If I Test Positive Privately?
If a private ECM swab test confirms you carry GBS, share this result with your midwife as soon as possible. They will note it in your maternity records and arrange for you to receive IV antibiotics when you arrive in labour. You do not need to have a caesarean section purely because of GBS carriage — a vaginal birth with appropriate antibiotic cover is the standard recommended approach.
Frequently Asked Questions
Will the NHS automatically test me for group B strep?
No. Routine GBS screening is not currently offered on the NHS to all pregnant women in the UK. However, if GBS is found incidentally during another test — such as a urine sample — your midwife will take action. You can also choose to pay for a private enriched culture medium swab, typically done at 35–37 weeks.
Can I get tested privately for GBS in the UK?
Yes. Private ECM swabs are available in the UK and are more sensitive than standard swabs. The test involves taking swabs from the vagina and rectum, which are sent to a laboratory. Results typically take a few days. If you test positive, inform your midwife so that IV antibiotics can be arranged for labour.
Does carrying GBS mean my baby will be affected?
No. Most babies born to mothers who carry GBS are completely healthy. The risk of a baby developing GBS infection is small, and that risk is reduced further with antibiotic treatment during labour. If you have concerns, speak to your midwife who can discuss your individual circumstances and what precautions are appropriate for you.
Speak to your midwife or GP for personalised advice about GBS testing and your care plan.
Further reading:
This article is for informational purposes only and does not constitute medical advice.
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