A reassuring start

Group B Strep (GBS) is very common, and the vast majority of babies born to GBS carriers are completely uninfected and well. This guide explains what GBS is, how testing works in the UK, and what happens if you test positive.

This information is for general guidance only.

It does not replace advice from your midwife, GP or maternity team. Read more about our approach.

Group B Strep in pregnancy: the UK guide

What is Group B Strep?

Group B Streptococcus (GBS, also called Strep B or Group B Strep) is a common bacterium found naturally in the digestive system and vagina of around 20 to 40 percent of women in the UK. It is not a sexually transmitted infection, and it causes no symptoms or harm to the carrier.

Most babies who come into contact with GBS during birth are completely unaffected. A small number can develop a serious GBS infection, most commonly in the first few days of life. This is what the UK approach to GBS aims to prevent.

GBS in numbers

20-40%

of UK women carry GBS naturally

1 in 1,750

UK babies develops early-onset GBS infection (days 0-6)

1 in 2,700

develops late-onset GBS infection (days 7-90)

Most babies

with GBS infection recover fully with prompt treatment

#1 cause

of life-threatening infection in UK newborns

UK testing policy

Important UK-specific point. Routine NHS screening for all pregnant women is not currently offered in the UK. The UK National Screening Committee has reviewed the evidence and concluded that a positive swab weeks before birth does not reliably predict carriage at delivery, and that universal screening could lead to many more women receiving unnecessary antibiotics. This policy is explained by the NHS guidance on Group B Strep.

This is different from the United States, where universal GBS screening at 35 to 37 weeks is standard. The UK GBS3 trial is currently gathering evidence on whether universal ECM testing should be adopted.

When GBS is tested for in the UK

  • Routine urine tests in pregnancy may detect GBS incidentally.
  • If GBS is found in urine, you will be treated and offered IV antibiotics in labour.
  • If GBS was found in a previous pregnancy, an ECM swab is offered at 35 to 37 weeks.
  • If you had a previous baby with GBS disease, IV antibiotics in labour are recommended.

Private testing option

You can pay for a private ECM swab test through Group B Strep Support (GBSS) at gbss.org.uk/test, typically £35 to £50.

The ECM (Enriched Culture Medium) test is more sensitive than a standard swab and should be done at 35 to 37 weeks, or earlier if preterm birth is anticipated.

A standard swab is not reliable for GBS. The test must specifically be an Enriched Culture Medium (ECM) test.

Risk factors for a baby developing GBS infection

  • Baby born before 37 weeks (the earlier, the higher the risk)
  • GBS found in urine during this pregnancy
  • GBS found in a previous pregnancy
  • Previous baby who developed GBS disease
  • High temperature during labour (38°C or above)
  • Prolonged rupture of membranes (waters broken 18 hours or more before birth)

Intrapartum antibiotics (IAP)

If you are offered IV antibiotics in labour, here is what to expect.

  • Antibiotic of choice: benzylpenicillin (Penicillin G) given intravenously.
  • Timing: first dose as soon as possible once labour begins, then every 4 hours until delivery.
  • Penicillin allergy: a cephalosporin antibiotic is used instead. If you have had a severe reaction (anaphylaxis) to penicillin, tell your midwife early so an alternative can be planned.
  • Before labour: antibiotics are not given before labour starts (except to treat a GBS urinary tract infection). They are only given once you are in active labour.
  • Planned caesarean: if your membranes are intact, IAP is not required even if you are a GBS carrier.

After birth: what to expect for your baby

If you received IV antibiotics at least 4 hours before birth, your baby is born at full term, and appears well, no extra monitoring is routinely required.

If antibiotics were given less than 4 hours before birth, or not at all, your baby will be monitored for at least 12 hours for any signs of GBS infection.

Reducing the risk: practical steps

  • Tell your midwife early if you have previously had a GBS-positive result, or a baby affected by GBS.
  • Consider a private ECM test at 35 to 37 weeks if you want more information. Ask your midwife about the ECM test specifically.
  • Include your GBS status in your birth plan so every team member is aware.
  • Make sure any birth centre or hospital you attend knows your status on arrival.
  • In labour, if you are GBS positive, aim to get to hospital once contractions are regular so there is time for antibiotics to take effect.

Support and information

Group B Strep Support (GBSS)

gbss.org.uk | 01444 416176

The UK charity for GBS awareness. Offers a helpline, detailed information, guidance on private testing, and support for families affected by GBS.

Related guides and tools

Your NHS antenatal appointments→ Include GBS in your birth plan→ Hospital bag checklist→ Signs that labour has started→

A note from our team

This guide reflects NHS UK, Royal College of Obstetricians and Gynaecologists (RCOG) and Group B Strep Support (GBSS) guidance. Your midwife and obstetric team are the best source of advice for your specific pregnancy. Read more about us.

Frequently asked questions

Does everyone in the UK get tested for Group B Strep?
No. Routine NHS screening for all pregnant women is not currently recommended in the UK. The UK National Screening Committee has reviewed the evidence and concluded that a positive result weeks before birth does not reliably predict status at delivery. Instead, antibiotics are offered based on known risk factors. The GBS3 trial is gathering evidence on whether universal ECM testing should be adopted.
How do I get tested for GBS in the UK?
GBS may be found incidentally on routine urine tests during pregnancy. If you have had GBS in a previous pregnancy, you will be offered an ECM swab test at 35 to 37 weeks. You can also pay for private ECM testing through Group B Strep Support at gbss.org.uk/test. A standard swab is not reliable for GBS, so make sure any private test is specifically an Enriched Culture Medium (ECM) test.
What is an ECM swab test?
The Enriched Culture Medium (ECM) test is the gold standard test for GBS carriage. Two swabs (one vaginal, one rectal) are placed into a special growth medium that allows GBS to grow and be identified. It is more sensitive than a standard swab. The test should be done at 35 to 37 weeks, or earlier if preterm birth is expected.
Do I need antibiotics in labour if I have GBS?
Intravenous antibiotics in labour (IAP) are recommended if you have had GBS in your urine this pregnancy, if a swab at 35 to 37 weeks is positive, if you have had a previous baby with GBS disease, or if risk factors develop (preterm labour, high temperature, or waters broken 18 hours or more before birth). If you are having a planned caesarean with intact membranes, antibiotics are not required.
Can I have a home birth if I am GBS positive?
This is best discussed with your midwife. GBS positivity is not an automatic reason to change plans, but IV antibiotics in labour are only given in a hospital setting. Some people choose to transfer to hospital for antibiotics and return home, or plan a hospital birth with early discharge. The right answer depends on your individual circumstances.
What are the signs of GBS infection in a newborn?
Rapid or laboured breathing, a high or low temperature, floppiness or unusual irritability, not feeding well, an unusually high-pitched cry, or pale or mottled skin. If you see any of these signs after leaving hospital, seek urgent medical help immediately. GBS infection can progress quickly, so do not wait.
Will antibiotics in labour affect my baby?
IV penicillin given to you in labour has very few effects on the baby. A small amount crosses the placenta, which is what protects your baby from infection. Some research has linked antibiotics in labour to small changes in the baby's early gut bacteria, but this does not outweigh the significant benefit of preventing serious GBS disease when risk factors are present.