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Group B Streptococcus Infection (GBS)

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What is Group B Strep?

Group B Streptococcus, often abbreviated as GBS, is one of many bacteria that can be present in our bodies. It usually causes no harm. This situation is called carrying GBS or being colonised with GBS. GBS is commonly found in the digestive system and the female reproductive system. It’s estimated that about one in four pregnant women in the UK carry GBS. Most pregnant women who carry GBS bacteria have healthy babies. However, there’s a small risk that GBS can pass to the baby during childbirth. Most babies are unaffected, but a small number can become infected.

Rarely, GBS infection in newborn babies can cause serious complications that can be life-threatening.

Extremely rarely, GBS infection during pregnancy can also cause miscarriage, early labour or stillbirth.

Are pregnant women tested for GBS?

Currently the evidence suggests that screening all pregnant women routinely would not be beneficial overall. You can be tested privately for GBS, however, positive test results may lead to interventions which are potentially unnecessary. This involves both a vaginal and rectal swab.

As GBS can cause urine infection in pregnant women, GBS infection may be detected by taking a mid-stream urine sample, sometimes referred to as an MSU, which is then sent to a laboratory for analysis. Urine infection caused by GBS should be treated with antibiotics.

GBS may sometimes be detected during pregnancy in the course of taking a vaginal swab for signs of other infections. However not all vaginal swabs will detect GBS so it is important to be aware that a negative swab test does not guarantee that you are not a carrier of GBS.

If GBS is detected either in urine or swabs during your current pregnancy you will be offered intravenous antibiotics in labour. Routine testing for GBS is not necessary

Early-onset GBS infection

If a baby develops GBS infection less than seven days after birth, this is known as early-onset GBS infection. Most babies who become infected develop symptoms within 12 hours of birth.

It’s estimated that about one in 2,000 babies born in the UK and Ireland develops early-onset GBS infection. This means that every year in the UK, out of 680,000 births, around 340 babies will develop early-onset GBS infection.

Risk factors for infection

Your baby may be at higher risk of bacterial infection if:

  • You have previously had a baby who had a GBS infection;
  • GBS has been found in your urine or a vaginal or rectal swab during your current pregnancy;
  • Your waters broke 18 hours before the birth;
  • During labour your temperature is higher than 38°C, or you have
    a confirmed infection of the membranes or amniotic fluid called
  • Your baby is born before 37 weeks and your waters broke more than 18 hours before the birth;
  • You have confirmed bacterial infection such as septicaemia 24 hours before the birth, during labour or within 24 hours of the birth; or you had a multiple birth, (twins or more), and infection is suspected or confirmed in one of the babies.


A pregnant woman with risk factors may be offered intravenous antibiotics from the start of labour and at intervals until the baby is born. Intravenous means the medicine is injected directly into the bloodstream via a drip. Whether you are offered treatment during labour will depend on your individual risk factors. It is estimated that this preventive treatment reduces the risk of infection by approximately 90%.

Women with risk factors whose waters break before labour starts should be assessed on labour ward as soon as possible. Induction of labour and intravenous antibiotics will be offered promptly, waiting for 24 hours for labour to start is not suitable in these cases.

When will antibiotics be offered?

You will be offered antibiotics during labour if:

  • GBS is found in your urine during your pregnancy
  • You have previously had a baby who had a GBS infection
  • During labour your temperature is 37.5°C or higher on two occasions, or you have a confirmed infection of the membranes or amniotic fluid called chorioamnionitis
  • Your baby is born before 37 weeks and your waters broke more than 18 hours before the birth
  • You have a bacterial infection confirmed, for example septicaemia, 24 hours before the birth.

When treatment with antibiotics is not necessary

  • If GBS was detected in your vagina in a previous pregnancy and the baby was not affected.
  • Your waters breaking more than 18 hours before the birth is the only risk factor.
  • If you have a planned caesarean section before you go into labour and before your waters break.

The reason antibiotics are not usually needed in these situations is because the risk to your baby of becoming infected with GBS is very low and because antibiotics do not reduce your chances of carrying GBS at the time of the birth.

Treatment for your baby

Antibiotics are not recommended for well babies who are born to mothers with risk factors and who have received antibiotics in labour at around 4 hours before birth. They will be monitored for at least 12-24 hours following the birth.

For well babies born to mothers with one risk factor who have not received antibiotic therapy in labour, for example, due to a quick labour, it is recommended that the baby is observed closely in hospital every two hours for 12 hours, blood test and antibiotics, it will usually take 48 hours for the blood results.

Antibiotics are recommended for well babies in the presence of multiple risk factors where the        mother did not receive antibiotics in labour until tests confirm that the baby does not have early-onset GBS. It will usually take 48 hours for the results of all tests to be available.

Antibiotics should also be given to babies where:

  • There are clinical signs of infection whether or not antibiotics were given in labour. In this case, antibiotics may be started as a precaution until the diagnosis is confirmed;
  • During labour your temperature is 37.5°C or higher on two occasions, or you have a confirmed infection of the membranes or amniotic fluid called chorioamnionitis;
  • You had twins, or more, and infection is suspected/confirmed in one of the babies;
  • You had a confirmed bacterial infection within 24 hours of the birth and are being treated.

When to seek medical help after the birth

If there were concerns about, or risk factors for, early onset neonatal infection you should seek medical help, for example from NHS Direct, your GP surgery or local Accident and Emergency department, if you are worried that your baby shows signs of the following:

  • Changes in behaviour, for example, inconsolable crying.
  • Being listless or unusually floppy.
  • Problems feeding/ tolerating feeds.
  • Abnormal temperature unexplained by the environment, for example, being unusually cold or hot.
  • Rapid breathing.
  • Change in skin colour

Useful resources

Please ask a health professional if you have any questions about the information contained here.

Publication Date: January 2021

Review Date: January 2024

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