Group B Strep

Written by

Rob Buist

Published on


Our mouths, our bottoms and our vaginas contain many bacteria. The overwhelming majority of these bacteria are harmless to our health. Group B Strep is a bacterium that lives in the vagina of 12-15% of Australian women. It is not a sexually transmitted disease (which means it is not the type of infection your mother warned you about when you were a teenager). Group B Strep does not usually cause any symptoms, and it is not harmful to women. However, if it is passed to a baby during a vaginal birth, it can rarely – extremely rarely – cause a serious infection in the newborn baby.

What does this mean for my baby?

Many babies will come into contact with Group B Strep during labour and birth and only a very small number of babies will become infected. Approximately 1% of babies exposed to Group B Strep at birth will develop an infection. It is therefore VERY rare. The majority of babies who come into contact with Group B Strep are not harmed. Of the babies that develop Group B Strep, a very small number of these babies will develop a serious infection such as pneumonia or meningitis.

Is there a test to see if my baby is at risk of contracting Group B Strep?

Yes. At around 35 weeks of pregnancy, you will be offered a vaginal bacteriology swab. This is a really simple test you can perform yourself – we just ask you to put a cotton bud just inside the entrance to your vagina. We will call you with your results within a few days.

How can my baby be protected from developing an infection?

If you have tested positive to Group B Strep on your vaginal swab at any time in pregnancy you will be offered antibiotics during your labour. These are administered into a plug in a vein in your arm, and do not prevent you moving around, or hopping into the shower or bath during labour. The usual antibiotic given for Group B Strep is penicillin; other antibiotics can be given if you are allergic to penicillin. You will also be offered antibiotics in labour if:

  • You have Group B Strep found in a urine sample
  • You have had a previous pregnancy affected by Group B Strep
  • You develop a temperature/fever during labour
  • Your waters have been broken for over 18 hours.
  • Your labour starts before 37 weeks gestation.

Are there risks with having antibiotics?

Side effects are extremely rare with intravenous antibiotics. Allergic reactions to antibiotics are vanishingly rare in women with no previous history of such allergies. In the extremely unlikely event of an allergic reaction occurring we are able to give you appropriate medication to treat the allergy. We believe that if you are positive for Group B Strep the risk of you suffering an allergic reaction to antibiotics is much, much less than the risk of your baby being harmed by Group B Strep.

Why don’t you give me antibiotics when we find out I am carrying Group B Strep, rather than waiting until I am in labour?

Good question. Logic would suggest that we should treat you and get rid of the Group B Strep once we find out about it. Unfortunately this approach does not work because the Group B Strep usually returns once you have been treated for it. This is why we only give you the antibiotics once you are in labour.

What if I come into hospital and give birth before the antibiotics can be administered?

Some babies can arrive very quickly. Whilst we recommend antibiotics in order to prevent a Group B Strep infection, it is important to remember that such infections are rare. If your baby is born before we can give you antibiotics we usually keep an extra close eye on your baby for signs of infection for the first 48 hours after birth. If there are other risk factors for infection (such as you having a fever in labour), we may give your baby one dose of antibiotics shortly after it is born.

Does being positive for Group B Strep affect my labour?

Not really. However, we prefer your baby to be born within 24 hours of your waters breaking if you have Group B Strep. (Once your waters have broken, the protective bag around your baby is broken and bacteria in your vagina can start migrating into the uterus). Accordingly, if you have Group B Strep and your waters have broken, but you are not in labour, we will usually recommend either inducing your labour contractions or starting you on antibiotics while we wait for labour to begin.

Do I need antibiotics for Group B Strep if I am having an elective Caesarean?

No. Some people call a Caesarean section a vaginal bypass procedure. A Caesarean performed before labour completely bypasses the vagina – and its bacteria!

This information sheet was adapted from The Royal Hospital for Women Group B Strep information sheet by our midwife Amanda Bartlett. As usual I take full responsibility for any errors or omissions.

– Rob