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The Importance of Screening for Group B Streptococcus in Pregnancy

31 March 2016

Group B Streptococcus, also known as GBS or Strep B infection, is a bacterium which is carried naturally in 20 to 30% of men and women. It usually lives in the gut or, in adult women, is often found in the vagina and because of this there is a risk that the bacteria can be passed to babies during pregnancy and birth. Carrying the GBS bacteria does not automatically mean that a baby will become infected and ill however, it does increase the chance.

Risk Factors

In the UK, 75% of GBS infections in babies from birth to six days, and nine out of 10 resulting deaths, follow deliveries where one or more of the associated risk factors were present. These indicators include pregnant women who have a high temperature during labour, labour starting or waters breaking prematurely, and having a previous baby infected with GBS.  Early recognition and treatment is important for the successful treatment of GBS.


In the UK, pregnant women are not routinely offered testing for GBS and the current policy for screening is centred on using a ‘risk factor’ approach to determining which women are most likely to be affected.  Sensitive tests designed to detect group GBS carriage are available, but rarely within the NHS. Women can choose to be screened privately however at specialist pregnancy clinics. The ECM (or Enriched Culture Medium) test is recognised as the ‘gold standard’ for detecting GBS carriage. Swab samples are taken from the lower vagina and just inside the rectum, which are then incubated in an enriched culture medium specifically designed to encourage the growth of GBS and so enhance its detection. The bacteria have to grow into a sizeable colony before they can be identified, so getting a result takes a minimum of 24 hours, and more usually two to three days to establish whether GBS has grown.  The test is usually done at around 35 to 37 weeks of pregnancy.


If a woman is carrying GBS during her pregnancy, then preventative action can be taken to minimise the chance of her newborn baby developing the infection. It is standard practice, if GBS is detected at any time during pregnancy, that women should be offered intravenous antibiotics from the start of their labour and at regular intervals until the baby is born.

If you are concerned about GBS you should speak to your GP, midwife or a specialist pregnancy clinic.

Mrs Santosh Mohindra is Consultant Sonographer at The Pregnancy and Gynaecology Clinic at HCA The Wilmslow Hospital, 52 Alderley Road. For more information or to make an appointment with Mrs Mohindra please call 01625 545 036.


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