Patient information

Group B Streptococcus (GBS) 

Group B Streptococcus (GBS) is the most common cause of life-threatening infections in newborn babies in the UK.  TDL provide a service to test for GBS that can be done in the comfort of your own home.

What is Group B Streptococcus (GBS)?

Group B Streptococcus is a naturally occurring bacterium carried by 20-40% of adults, usually without any symptoms or side-effects. It is commonly found in the gut and for up to 25% of women in the vagina. Carrying GBS does not present any symptoms in itself.

It can cause an infection in young babies during pregnancy and labour that can lead to sepsis and meningitis. GBS is not a sexually transmitted disease and having treatment does not stop you getting the bacterium again in the future.

Most GBS infections can be prevented by giving antibiotics intravenously (through a vein) at the onset of labour to all women who carry GBS. UK guidelines recommend mums should be offered these antibiotics in labour:

  • if GBS has been detected during the current or previous pregnancy
  • if a previous baby had GBS infection
  • if she is in preterm labour (before 37 completed weeks of pregnancy) or
  • if she has a fever in labour.

Another risk factor is waters breaking more than 18 hours before birth.  

Intravenous antibiotics in labour are highly effective at preventing GBS infection in newborn babies, reducing the risk for a newborn baby born to a woman carrying GBS from around 1 in 400 to around 1 in 5000. Oral antibiotics should not be given during pregnancy for GBS as they have not been shown to reduce GBS infection in babies.  

There are always small but potentially serious risks associated with taking antibiotics, and this needs to be fully discussed with your doctor or midwife.

Screening for GBS is not routinely offered in the NHS. Laboratory testing for GBS is carried out at The Doctors Laboratory ( following the method described in the UK Standards for Microbiological Investigations, using enriched culture medium (ECM).

Two swabs (lower vaginal and rectal) need to be cultured, ideally in the last five weeks of pregnancy, to best predict GBS carriage around the time of delivery.

When the ECM test is properly performed within 5 weeks of giving birth, a negative result was shown to be 96% predictive of not carrying GBS at delivery (4% of women acquired carriage between the test and birth) and a positive result 87% predictive of carrying GBS at delivery (13% of women lost carriage in that time). The test can be performed earlier, but isn’t as reliable at predicting carriage status over longer periods. It can be performed later, although the chance of the baby arriving before the result increases.

Testing for GBS needs to be included in the pregnancy and birth plan and discussed with the midwife, obstetrician or GP including the treatment plan if GBS is detected. UK guidelines recommend that, when GBS is detected during the current pregnancy, the woman should be offered intravenous antibiotics in labour. This will stop most GBS infections from developing in newborn babies.

Antibiotics may affect the GBS test result. If you are taking antibiotics, or have recently, discuss this with your midwife or doctor.

GBS carriage can come and go, though tests are very predictive for a period of 5 weeks or so. Testing is usually undertaken after 35 weeks of pregnancy. Two swabs need to be taken and sent to the designated testing laboratory the same day by Royal Mail Tracked 24 postage; delays in sending can affect the result. The swabs should be accompanied by a completed request form showing:

  • Patient’s name, address, date of birth and date sample taken. Please provide the address to where results are to be sent.
  • Mobile phone number if you would like also to receive results by text message.
  • Name and full address, phone and or fax number of midwife and/or obstetrician to whom positive results will be sent.

The result of the test will be available within 3 working days of receipt of swabs. Results will be sent to the patient and to the named healthcare professional.

£37.50  (this includes the request form, postal pathology pack, 2 swabs in non-nutritive transport medium, post paid return envelope and laboratory testing service).

Please contact The Doctors Laboratory

Tel: 020 7307 7373 Email:

The Doctors Laboratory is fully accredited with ISO 15189 Medical Laboratories, and has a long-standing reputation for the provision of pathology services to the private sector, industry and the public sector.

Group B Strep Support

Tel: 0330 120 0796  E-mail:  Website:

Group B Strep Support  is a UK charity providing accurate and up to date information on GBS for families and health professionals. Group B Strep Support endorses the availability of reliable prenatal testing and wants ECM testing to be available to all pregnant women through the NHS. The charity’s current leaflets are available from their website at or by post.

Registered charity No 1112065

If you are pregnant and want more information about Group B Strep, visit

Key medical references

NICE. Neonatal infection (early onset): antibiotics for prevention and treatment (CG149). National Institute for Health & Care Excellence Guidelines. 2012.

RCOG. Prevention of Early Onset Neonatal Group B Streptococcal Disease (3rd edition). Royal College of Obstetricians and Gynaecologists Guidelines 36. 13/09/2017. 

Public Health England Detection of Carriage of Group B Streptococci (UK Standards for Microbiology Investigations B 58). 2018.

Centers for Disease Control and Prevention. Prevention of Perinatal Group B Streptococcal Disease – Revised Guidelines from CDC: 2010. MMWR Reports & Recommendations 59 (2010).