Group B streptococcus (‘GBS’, or ‘group B strep’) is a type of bacteria that lives on our bodies.
It is very common and is part of the normal population of bacteria that we carry around in our intestines or vagina. If you happen to carry GBS while you are healthy, it is NOT considered a disease that needs to be treated. It is not a sexually transmitted infection.
About 20% of women have GBS in their vagina around the time of giving birth.
If GBS is present in the vagina at the time of labour, there is a chance that it will be passed to the baby. Most babies who catch GBS remain well, but some babies get very sick and need nursery admission and intravenous antibiotics in the first few days of life. This is called early onset GBS sepsis.
Without treatment, about 1 in 200 women with GBS will have a baby that develops a severe infection.
What can be done to prevent my baby getting sick from GBS?
Your baby can be protected from GBS disease if you have antibiotics during labour. These antibiotics pass across the placenta to the baby before it is born and help prevents severe infection during the first few days of life.
How will I know if my baby is at risk of GBS sepsis?
There are particular situations where the risk of GBS infection is increased. These include:
premature labour or if your waters break (rupture of membranes) before 37 weeks
fever above 38oC in labour (at any gestation)
if your waters have been broken for more than 18 hours (prolonged rupture of membranes)
if GBS is detected in your urine during pregnancy
a previous child with severe GBS infection
GBS detected on a vaginal swab performed within the past 5 weeks
If any of these risk factors are present, then your midwife or doctor should talk to you about receiving antibiotics in labour.
Some hospitals will test all pregnant women for GBS with a vaginal swab at around 36 weeks. Other hospitals only give antibiotics to women with specific risk factors, such as preterm labour or prolonged rupture of membranes.
You should talk to your doctor or midwife about which approach they use.
How do I take the antibiotics if I need them?
Penicillin is the most effective antibiotic against GBS. It is given during labour through an intravenous drip in your arm or hand. It provides the best protection if it is given at least four hours before the baby is born.
There is no need to treat GBS before labour if your waters have not broken. Women who are having a planned caesarean section without labour do not require specific treatment for GBS before the caesarean.
How is my baby checked for GBS sepsis after birth?
If you needed antibiotics in labour because of a chance of GBS
infection, your baby should have some additional observations
in the first two days of life to make sure there are no signs of
These include regular checks of the baby’s breathing, heart rate
and temperature. If you have any concerns about the condition of
your baby, you should alert your midwife or doctor. Your baby will
not routinely receive antibiotics unless there are signs of infection.
Are there any potential side effects from having antibiotics during labour?
As with any antibiotic, there is a very small risk of a severe allergic reaction (anaphylaxis). This risk is less than 1 in 2000, which is lower than the risk of a baby dying from GBS infection. Other milder side effects for the mother include rash, nausea, or diarrhoea.
If you have a known penicillin allergy, there are alternative antibiotics that can be used. Please remind your midwife or doctor about your drug allergy before accepting any medication.
There are no known serious adverse effects for the baby. The antibiotic treatment should not affect the way you plan to feed your baby.
To swab or not to swab?
There remains some controversy about whether to swab and test all women for the presence of GBS in the vagina and then subsequently treating all those women during their labour. Remember that 1 in 5 (20%) of women will test positive, but only about 1 in 200 babies will have a severe infection. However, severe GBS infection is a very serious infection when it occurs. It is an important topic to discuss with doctor or midwife. If you have any further questions about GBS, please ask your doctor or midwife.
DISCLAIMER: This information is intended to be used as a guide of general nature, having regard to general circumstances. The information presented should not be relied on as a substitute for medical advice, independent judgement or proper assessment by a doctor, with consideration of the particular circumstances of each case and individual needs. This information reflects information available at the time of its preparation, but its currency should be determined having regard to other available information. RANZCOG disclaims all liability to users of the information provided.