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Strep B in pregnancy

Group B streptococcus (GBS) is sometimes also called 'strep B' or 'Group B strep'. It is one of many germs (bacteria) that live in our bodies and usually causes no harm. GBS is not a sexually transmitted infection.

If you carry GBS during pregnancy, your baby will usually not develop any problems. However GBS can, rarely, cause serious infections in babies, including sepsis, pneumonia or meningitis.

If your baby has GBS infection, early diagnosis and treatment are essential as any delay can be very serious or even fatal. If your baby becomes very unwell or develops any signs that suggest possible GBS infection, they should be treated with antibiotics straightaway.

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GBS in pregnancy symptoms

Most women carrying GBS will have no symptoms. Carrying GBS is not harmful to you, but it can affect your baby around the time of birth. GBS can occasionally cause serious infection in newborn babies and, very rarely, during pregnancy or labour.

GBS infection may cause sepsis, pneumonia and/or meningitis. It can also lead to bone infection (osteomyelitis) and joint infection (septic arthritis). Therefore your baby may develop symptoms caused by these types of infections. See the links for more details.

Early-onset GBS

Most babies who develop GBS infection become unwell in the first week of life, usually within the first 12 hours after birth. This is called early-onset GBS infection.

Babies with early-onset GBS infection may:

  • Develop noisy breathing and grunting.

  • Seem to have to work hard to breathe, and breathe more rapidly.

  • Be very sleepy or unresponsive.

  • Constantly cry and seem distressed.

  • Be unusually floppy.

  • Not feed well.

  • Have a high or a low temperature, with their skin feeling very hot or cold.

  • Show changes in their skin colour or have blotchy skin.

  • Have an abnormally fast or slow heart rate.

If you notice any of these signs, you are concerned that your baby is very unwell and may have a serious infection, or are worried about your baby for any reason, you should contact a healthcare professional immediately.

Late-onset GBS

Late-onset GBS infection affects babies between seven days and three months after birth. Late-onset infection is less common than early-onset infection but up to a third of GBS infections in babies are late-onset. Infection in babies older than 1 month is very uncommon and it is very rare after the age of 3 months.

Typical signs of late-onset Group B strep infection are similar to those associated with early-onset infection.

How common is GBS?

  • GBS is carried in the vagina and bowel of about 3 in 10 women in the UK.

  • GBS is the most common cause of severe infection in newborn babies. It is the most common cause of meningitis in babies under the age of 3 months.

  • On average in the UK, about 1 in 2,000 newborn babies are diagnosed with early-onset GBS infection.

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Testing for GBS

Standard tests using swabs and urine samples are not very efficient at picking up GBS. The enriched culture medium (ECM) test is more accurate.

Standard testing carries a risk of a 'false negative' test - where you are advised that the result is negative even though you are carrying GBS. If a standard swab or urine sample shows GBS, it is highly likely to be correct.

The ECM test is not yet available everywhere within the NHS.

GBS pregnancy risks

GBS infection is more likely to happen if:

  • Your baby is born preterm (before 37 completed weeks of pregnancy) - the earlier your baby is born, the greater the risk.

  • You have previously had a baby affected by GBS infection.

  • You have had a high temperature or other signs of infection during labour.

  • You have had any positive urine or swab test for GBS in this pregnancy.

  • Your waters have broken more than 24 hours before your baby is born.

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Can you be tested for GBS in pregnancy?

GBS is sometimes found during pregnancy when you have vaginal or rectal swabs or a urine test.

If GBS was found in a previous pregnancy but your baby was unaffected then there is a 1 in 2 chance that you will be carrying GBS in any future pregnancy. You should be offered a ECM swab test between 35 and 37 weeks of pregnancy to see whether you are carrying GBS.

In the UK, the NHS does not routinely offer all pregnant women screening for GBS.

Can the risk of GBS infection in your baby be reduced?

Most early-onset GBS infections (in babies aged 0-6 days) can be prevented by giving intravenous antibiotics during labour to women whose babies are at particular risk of GBS infection:

  • A urine infection caused by GBS should be treated with antibiotic tablets straightaway and you should also be offered antibiotics through a drip during labour.

  • You should be offered antibiotics through a drip during labour if you have had a GBS-positive swab or urine test. See below for more information

  • If you have previously had a baby who was diagnosed with GBS infection, you should be offered antibiotics through a drip when you are in labour.

  • If you are known to have had GBS in a previous pregnancy but your baby was not affected, you should be offered the option of intravenous antibiotics during labour or ECM testing for GBS between 35 and 37 weeks of pregnancy, with intravenous antibiotics in labour if the test is positive.

  • If your waters break after 37 weeks of your pregnancy and you are known to carry GBS, you will be offered induction of labour as soon as possible. This is to reduce the time that your baby is exposed to GBS before birth. You should also be offered antibiotics through a drip straightaway.

  • Even if you are not known to carry GBS, if you develop any signs of infection in labour, you will be offered antibiotics through a drip that will treat a wide range of infections, including GBS.

  • If your labour starts before 37 weeks of your pregnancy, you should be given antibiotics through a drip even if you are not known to carry GBS.

If GBS has been found, when should you have antibiotics?

If you are found to carry GBS in your vagina or rectum, treating you with antibiotics before your labour begins does not reduce the chance of your baby developing GBS infection. You do not need antibiotic treatment until labour starts.

When your labour begins, you will be offered antibiotics through a drip to reduce the chance of your baby being infected. These antibiotics reduce the risk of your baby developing a GBS infection in their first week of life from around 1 in 400 to 1 in 4,000.

If GBS is found in your urine then you will need antibiotics, as soon as it is diagnosed, to treat your urinary tract infection. You will also be offered antibiotics through a drip during labour to prevent GBS infection in your baby.

If you are having a planned caesarean section and you carry GBS, you do not need antibiotics to prevent GBS infection in your baby unless labour has started or your waters have broken. However all women having a caesarean section are offered antibiotics at the time of the operation to reduce the risk of a wide variety of infections.

How will your baby be monitored after birth?

If your baby is born at full term (after 37 completed weeks) and you received antibiotics through a drip in labour at least four hours before giving birth then your baby does not need special monitoring after birth.

If your baby is at higher risk of GBS infection and you did not get antibiotics through a drip at least four hours before giving birth then your baby will be monitored closely for signs of infection for at least 12 hours. This will include assessing your baby's general well-being, heart rate, temperature, breathing and feeding.

If you have previously had a baby affected by GBS infection then your baby will be monitored for 12 hours even if you had antibiotics through a drip in labour.

The chance of your baby developing GBS infection after 12 hours is very low and neither you nor your baby will need antibiotics after this time unless you or your baby become ill.

How is GBS infection in babies treated?

If it is thought that your newborn baby may have an infection, tests will be done to see whether GBS is the cause. This may involve taking a sample of your baby's blood, or a sample of fluid from around your baby's spinal cord (a lumbar puncture).

Babies with signs of GBS infection or babies who are suspected to have the infection should be treated with antibiotics as soon as possible. Treatment will be stopped if there is no sign of infection after at least 36 hours, and all the tests are negative.

It is safe to breastfeed your new baby. Breastfeeding has not been shown to increase the risk of GBS infection, and it offers many benefits to both you and your baby.

What is the outcome?

Although GBS infection can make your baby very unwell, early treatment means that most babies will recover fully. However about 1 in 20 babies who develop early-onset GBS infection will die and 1 in 14 of the survivors will have a long-term disability.

On average in the UK, every month:

  • 43 babies develop early-onset GBS infection.

  • 38 babies make a full recovery.

  • 3 babies survive with long-term physical or mental disabilities.

  • 2 babies die from their early-onset GBS infection.

If you have had a baby affected with GBS infection there is an increased risk that any future baby will also be affected. This is why you will be offered antibiotics during labour if you have had a previous baby with GBS infection.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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