Group B streptococcus (GBS) is one of many bacteria that normally live in our bodies and usually cause no harm. This is called GBS carriage, colonisation with GBS or carrying GBS.
About a quarter of pregnant women in the UK are estimated to carry GBS in their vagina and rectum. As a result, many babies come into contact, and are colonised with, GBS around the time of labour and birth. The vast majority of babies are unaffected, but a small number become seriously ill with GBS infection.
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When this infection occurs in the first week of a babys life, it is known as early-onset GBS infection. Infections developing after the first week and up to three months of age (after which time GBS infection is extremely rare) are referred to as late-onset GBS infection. Late-onset GBS infection is not usually associated with the pregnancy and is not dealt with here. (For information on late-onset GBS infection, see our streptococcal infections health encyclopaedia article).
Early-onset GBS infection
It is estimated that approximately 1 out of every 1,600 babies born in the UK and Ireland develops early-onset GBS infection. This means that every year in the UK (with 700,000 births per year) around 440 babies will develop early-onset GBS infection.
GBS infections can cause blood poisoning (septicaemia), infection of the lung (pneumonia) or infection of the lining of the brain (meningitis), and each of these can be life threatening. Sadly, even with the best medical care, 1 out of every 10 babies diagnosed with early-onset GBS infection will die (approximately 44 babies a year).
However, if pregnancies at increased risk of GBS infection are identified and appropriately managed, most early-onset GBS disease in newborn babies could be prevented.
Identification of pregnancies at increased risk
Following the publication of the Royal College of Obstetricians and Gynaecologists (RCOG) guideline on early-onset GBS infection, healthcare professionals are being encouraged to use clinical risk factors to identify pregnancies which are more likely to result in early-onset GBS infection.
Approximately 60% of cases of early-onset GBS infection are associated with these identifiable risk factors and it is likely that the majority of severely affected cases could be prevented by targeting this group.
Management of pregnancies at increased risk
Intravenous antibiotics from the start of labour, and at intervals until delivery, are highly effective at reducing the risk of early-onset GBS infection in the baby. It is estimated that, with this preventive treatment, the risk of a baby developing early-onset GBS infection is reduced by approximately 90%.
The RCOG recommends the following approach to each risk factor:
 You have previously had a baby who had GBS infection - you should be offered antibiotics during labour. If you carried GBS during a previous pregnancy and your baby did not develop a GBS infection, treatment during labour is not recommended.
GBS has been found on swabs from your vagina and/or rectum which have been taken for another reason - your healthcare professional should discuss the possibility of antibiotic treatment during your labour with you. Treatment before labour or before your waters break does not reduce your chance of carrying GBS at the time of the birth.
GBS has been found in your urine during your current pregnancy - you should be offered antibiotics in labour after discussion with your healthcare professional.
Your baby is at higher risk of developing GBS infection. This may be because:
you have a temperature of over 38C (100.4F) in labour,
you go into preterm labour (before 37 completed weeks of pregnancy),
your waters have broken prematurely,
or your waters have broken for more than 18 hours.- your healthcare professional should discuss with you the option of antibiotic treatment during labour.
When antibiotics are used in labour to reduce the risk of early-onset GBS infection, penicillin is usually given. Clindamycin is used as an alternative for those mothers allergic to penicillin. You must inform the healthcare professional involved in your care if you have ever had an allergic reaction to penicillin or any other antibiotic.
Antibiotic treatment is not recommended if you plan to have a Caesarean and this takes place before labour begins and your waters have not yet broken.
Screening and testing for GBS in pregnancy
A policy of screening all pregnant women for GBS carriage during pregnancy is not recommended in the UK. There are several reasons for this. One is concern that, given the relatively low risk associated with most cases of GBS carriage, a positive test may result in unnecessary and potentially harmful treatment.
However, there may be circumstances which prompt healthcare professionals to find out if you carry GBS. If you are offered a test to detect GBS carriage it is important that you understand the purpose of the test, are satisfied that it is relevant to your care and are clear about the implications of having a positive and negative result.
The most sensitive testing method requires swabs to be taken from both your vagina and rectum, which are then processed in a laboratory in a special solution. This solution is referred to as an enriched culture medium. Although some hospitals use this process, it is not widely available within the NHS. The test is available privately.
GBS carriage can come and go, but a result from a sensitive test done a few weeks before delivery is relatively reliable at predicting whether or not you will carry GBS around the time of the birth. This does not mean that your baby will be affected.
When no other risk factors are present, about 1 in every 500 babies born to mothers with a positive test is likely to develop early-onset GBS infection. A negative test result, particularly if taken early in pregnancy or which has not used the sensitive method, does not guarantee that you will not be a carrier of GBS around the time of delivery.
After your baby is born
Most babies born to mothers who carry GBS are born healthy. If it is thought that a baby has a GBS infection, as opposed to being simply colonised with GBS, samples of the babys blood or fluid from the spinal cord can be tested. Healthy babies do not need tests for GBS or treatment.
Intensive care and intravenous antibiotics successfully treat most babies with GBS infection, most of whom will make a full recovery.
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