Strep B (group B streptococcus)

Strep B (Group B streptococcus) is a common bacteria found in the vagina, urine or rectum (back passage).

It's normally harmless and most people will not realise they have it.

It's usually only a problem if it affects:

  • pregnant woman – it could spread to the baby
  • newborn babies – it can make them very ill
  • elderly people or those who are already very ill – it can cause repeated or serious infections

This page focuses on strep B in pregnancy and babies.

Strep B in pregnancy

Strep B usually causes no harm to you or your baby.

It's not routinely tested for during pregnancy. But some hospitals may offer you a rapid test if your labour needs to be induced or if your waters have broken.

You might find out that you have strep B after a urine test, rectal swab or vaginal swab during pregnancy.

Risks in pregnancy

In rare cases, strep B can be passed to a baby during birth and make them ill.

Read more about the risk of strep B to your baby

Your baby may be at higher risk of developing strep B if:

  • they are born prematurely
  • you get a high temperature (38 degrees Celsius or higher) during labour
  • you have tested positive for strep B during this pregnancy
  • you get an infection during labour or birth
  • you have previously had a baby with strep B
  • your waters break more than 24 hours before your baby is born

Signs of strep B in women

Women who carry strep B do not have any symptoms.

If you're worried about strep B, talk to your midwife or GP.

If you have strep B

If tests find strep B, or you have had a baby that's had it before, you may need extra care and treatment.

You may be advised to:

  • review your birth plan with your midwife - the safest option may be to give birth in hospital
  • contact the hospital as soon as your waters break or when you think you are in labour
  • medically induce your labour if your waters break after 37 weeks. This will reduce the time your baby is exposed to strep B before birth
  • have antibiotics through a drip during the labour to reduce the chances of your baby becoming ill
  • take a course of antibiotic tablets. This may be needed if strep B is found in your urine and your GP or obstetrician thinks you have a urine infection
  • stay in hospital for longer than planned so your baby can be monitored

Antibiotics used for strep B are safe to take during pregnancy and birth. Always tell your prescribing doctor if you are allergic to any antibiotics.

If you are breastfeeding

It is safe to breastfeed your baby if you have strep B.

Complications of strep B in pregnancy

Complications of strep B for pregnant women are very rare, but can include:

  • urinary tract infections
  • womb infections
  • sepsis - where infection spreads through the blood

Future pregnancies

If your baby is diagnosed with strep B, you will be offered antibiotics during any future births. This is to reduce the risk of strep B in your next baby.

If you were diagnosed with strep B during pregnancy but your baby did not get it, your obstetrician and midwife will advise you. They'll usually advise you to be tested for strep B during your pregnancy as there is a 1 in 2 chance that you could be carrying it again.

Strep B in babies

In rare cases, strep B can be passed to a baby during birth and make them ill.

If your baby gets a strep B infection, they'll usually develop symptoms within 7 days of being born. This is sometimes called early-onset strep B. It sometimes causes severe health complications.

Babies can also develop a strep B infection 7 or more days after they are born. This usually means they didn't catch the infection during birth.

A strep B infection is extremely rare after the age of 3 months.

Signs of strep B in babies

Signs of strep B in babies can include:

  • feeling limp when held (floppy)
  • being sleepy or unresponsive
  • not feeding or not keeping milk down
  • breathing problems
  • high or low temperature
  • fast or slow heart rate
  • crying a lot

Urgent advice: Contact your maternity unit or hospital immediately if:

  • you notice any of these signs

Tell them you're concerned about strep B.

If your baby may have strep B

If your baby may have strep B, they'll be monitored in hospital. They'll be given antibiotics. If tests show that your baby does not have strep B, the antibiotics can be stopped.

Your baby may need another test called a lumbar puncture. This is when a sample of fluid is taken from around their spinal cord.

Complications of strep B in babies

Most babies recover fully. But complications can sometimes cause long term disabilities.

1 in 10 babies with strep B complications will die from the infection.

Strep B in newborn babies can cause:


Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 8.

Page last reviewed: 30 April 2021
Next review due: 30 April 2024