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Group B Streptococcus infection during pregnancy

group; streptococcus; strep; GBS; bacteria; infection; sepsis; vagina; vaginal; pneumonia; chorioamnionitis;



What is Group B Streptococcus – GBS?

It is normal to have a large number of different bacteria growing in the vagina of a healthy woman.

  • About 15% of women have a type of bacteria called Group B Streptococcus, or GBS, as part of these normal vaginal bacteria. 
  • GBS is not sexually transmitted, nor is GBS a sign of poor hygiene.

How does GBS affect me or my baby?

  • GBS doesn't cause any symptoms or problems for the woman. 
  • For reasons that are not fully understood, about 1% of babies born to a mother with GBS become infected during labour or at the time of birth.  
  • This can cause serious life-threatening infection in the baby's blood (sepsis), lungs (pneumonia) or brain (meningitis).

How do I find out if I have GBS?

  • When your urine is tested early in your pregnancy, it may show positive for GBS.
  • If it is not positive for GBS, it is recommended that an ano/vaginal swab be taken when you are 36 weeks pregnant. The swab is usually done by you and you will be instructed on how to obtain the sample. You will receive the result at your next antenatal appointment.

What increases the risk of my baby getting GBS?

The chance of your baby becoming ill with a GBS infection increases if the following risk factors are present:

  • If you have a preterm labour (go into labour before 37 weeks)
  • If you experience premature rupture of membranes (your waters break before 37 weeks)
  • If you are known to be GBS positive or your GBS status is unknown, and your waters are broken for more than 18 hours before the birth of your baby
  • If you have had a previous baby ill with a GBS infection

If any of these factors are present, research shows that antibiotics during labour will significantly reduce the chances of your baby getting seriously sick with a GBS infection.

Will my partner need treatment if I have GBS?

Because GBS is not sexually transmitted, your partner will not need treatment.

Will I need treatment if I have GBS?

If you are GBS positive, current research recommends that you have an antibiotic (generally penicillin, four hourly) during your labour.

  • The antibiotic is given intravenously (through a vein in your arm) but doesn't involve you being connected to a drip.
  • Your baby is best protected from becoming ill with a GBS infection if you have had at least 1 dose of antibiotics, 4 or more hours before the birth. If this is done, the risk of your baby becoming ill reduces from 1 in 100 (1%) to 1 in a 1,000 (0.1%).
  • This means it is highly advisable to come into the hospital early rather than late in your labour.

If you are GBS positive and your waters have broken but you are not in labour, your baby is less likely to become ill with a GBS infection if your labour is less than 18 hours long. Thus induction of your labour will be recommended.

  • In this case, induction involves having a hormone drip (syntocinon) put into a vein in your arm.
  • The hormone level via the drip is slowly increased until you are labouring well.

If none of the risk factors for infection are present and you have had adequate antibiotics, your baby will be closely monitored for any signs of illness. You will also be taught what signs and symptoms to look for. As long as your baby remains well, your baby will be able to stay with you.

Are there any risks associated with having an antibiotic during labour?

  • Any medication can have side-effects. Mild reactions to penicillin (such as rash) occur in less than 10% of people.
  • Severe allergic reaction (anaphylaxis) occurs in only 1 in 10,000 to 1 in 30,000 women. Effective treatment is available if this should occur.
  • If you know that you are allergic to Penicillin, notify staff and a different antibiotic will be given.

Babies who need antibiotics

Your baby will need treatment if:

  • The sac in which your baby floats before labour is infected, (this is called chorioamnionitis)
  • Your baby is unwell or shows signs of possible infection
  • Your baby's blood count is abnormal (a blood count is done if there are any risk factors for infection)
  • There are any increased risk factors (see above) and you have not had at least one dose of antibiotics four or more hours prior to the birth of your baby.

If I have any questions, who can I speak to?

If you would like further information on GBS, talk to your doctor or midwife.

You can also find out more information from the South Australian Perinatal Practice Guideline


Women's and Children's Hospital (South Australia) 'Group B Streptococcus'. 2016

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The information on this site should not be used as an alternative to professional care. If you have a particular problem, see your doctor or midwife.


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