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Group B strep test

8-minute read

If your baby suddenly develops very high fever with vomiting, call triple zero (000) and ask for an ambulance or go to the nearest hospital emergency department.

Key facts

  • Group B streptococcus (GBS) is part of the normal bacteria that lives in our body. It is most commonly found in the intestines, rectum, urethra or vagina.
  • It usually causes no health concerns or symptoms.
  • If you are pregnant and have GBS, bacteria can pass to your baby before or during a vaginal birth. In a small number of cases, this may make your baby sick.
  • You may be offered a test to check if you have GBS, which involves taking a swab of your vagina at around 35 to 37 weeks of pregnancy.
  • If you are a GBS carrier or if you develop risk factors for GBS infection, intravenous antibiotics during labour can reduce the risk of GBS colonisation and an early GBS infection in your baby.
  • Testing and treatment for GBS is your choice and should be done in consultation with your care provider.

What is GBS?

Group B streptococcus (GBS) is one of many bacteria that normally live in our bodies. GBS is commonly found in the intestines, rectum, urethra, or vagina. Many people have it, and it usually causes no health concerns or symptoms. This bacterium is transient, meaning that it comes and goes from your body. GBS is not sexually transmitted. Being a carrier of GBS in pregnancy is not usually harmful to you but it can cause infection in some babies.

Carrying GBS, also known as GBS colonisation is not the same as having a GBS infection.

What could GBS mean for my baby?

Many babies come into contact with GBS during labour or around the time of birth. Most of these babies won’t become unwell. However, if you carry GBS, there is a small chance (about 1 in 1000) that your baby will develop GBS infection in the first week after birth. This is known as ‘early onset GBS infection’.

GBS can cause infections such as pneumonia, blood poisoning (septicaemia), or meningitis (an infection around the brain) in babies. However, with early detection and treatment using intravenous antibiotics, most babies fully recover. A very small number of babies who become infected may have long-term disability and some don’t survive.

Can GBS infection be prevented?

Unfortunately, there is no way to completely prevent GBS infection in babies. However, early detection and treatment with antibiotics can reduce the chance of your baby becoming very unwell.

How is GBS found?

GBS may be found during a routine antenatal test. It can be found in urine or more commonly, when you have a vaginal or rectal swab testing specifically for this bacterium.

There is no standard practice for testing for GBS in Australia, but universal screening for the GBS bacteria is most common. This means that all women will be offered to test for GBS bacteria during pregnancy. Some healthcare providers may only test for GBS if you have risk factors that make GBS infection more likely.

The test can only find GBS if the bacteria is there at the time of testing. Because GBS bacteria comes and goes from your body, routine screening for this bacteria may not detect GBS in everyone who has it during pregnancy.

Testing for GBS involves taking a swab of the inside of the vagina and/or rectum. You can usually do this test yourself, but if you prefer your doctor or midwife can do this for you. The swab is usually taken between 35 to 37 weeks of pregnancy.

Speak to your doctor or midwife to understand how GBS is tested and managed at your care provider. They can help you to decide if this test is right for you.

Questions you may want to ask your doctor

  • What are the risks and benefits to me and my baby if I test for GBS?
  • If I have GBS, what does this mean for my pregnancy and birth?
  • What is the rate of GBS infection in newborn babies?
  • Can my baby become unwell if my test is negative?

What are the risk factors for early onset GBS infection?

Babies are more likely to become infected with GBS if:

  • they are born prematurely
  • your waters break before 37 weeks of pregnancy
  • you give birth more than 18 hours after your waters break
  • you have a fever (over 38°C) while in labour
  • you've had a previous child with severe GBS infection
  • a urine test during pregnancy detected GBS
  • a swab taken no more than 5 weeks earlier detected GBS

How is GBS treated?

If your GBS test is positive, or if you have risk factors as listed above, your doctor or midwife will probably recommend that you have intravenous antibiotics when your waters break or when labour starts. If your waters break before your labour starts your healthcare team may recommend inducing labour.

The antibiotic given is usually penicillin, but other options are available if you are allergic to penicillin. The antibiotics pass through the placenta and into your baby’s blood. This reduces your baby's chances of GBS colonisation and infection.

There is usually no need for screening or treatment with antibiotics for GBS before a planned caesarean, because the baby will not pass through your vagina.

What happens after the birth?

All babies are monitored for the first couple of days for signs of infection. Your baby’s health team will monitor their heart rate, breathing and temperature to check they are well. The chance of your baby being infected with GBS is very low.

Signs that your baby is not well may include:

  • abnormal breathing sounds, such as ‘grunting’ with each breath out
  • difficulty breathing or breathing too fast or slow
  • sleepiness and not interested in feeding
  • vomiting
  • having trouble keeping their temperature at the right level (being too hot or too cold)
  • looking pale or blotchy
  • floppy arms and legs

If you notice any of these signs in hospital or at home, it’s important that you contact your healthcare provider straight away.

What is late-onset group B strep?

Rarely, babies can develop GBS infection weeks or months after birth. This is called ‘late onset group B strep'. They become seriously unwell quite quickly with fevers, vomiting and difficulty feeding. Unfortunately, the group B strep test and use of antibiotics during labour doesn’t prevent a baby developing late-onset group B strep infection.

If your baby's condition deteriorates quickly, call triple zero (000) and ask for an ambulance or go to the nearest hospital emergency department.

Where can I get more information about GBS?

If you want more information about GBS, or if you have any concerns about your baby, call Pregnancy, Birth and Baby on 1800 882 436 to speak to a maternal child health nurse, or talk to your midwife or doctor.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

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Last reviewed: September 2022

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