Group B Streptococcus


What is Group B Strep?

Streptococcus is a bacteria that lives in different parts of the body. A strain of streptococcus, called Group B Strep or GBS for short, is often found in the bowels and vaginas of healthy women. Around 15-25% of pregnant women carry GBS.

What problems can Group B Strep cause in the mum?

GBS rarely causes major problems for healthy pregnant women with no underlying medical problems.

Sometimes it can cause a urinary tract infection. If GBS is detected in the urine of a pregnant woman, it should be treated with a course of oral antibiotics, whether or not the woman has any symptoms.

After delivery, GBS can occasionally cause an infection in the mother. This is more likely in women who had a long, difficult labour or needed an emergency caesarean section. GBS can cause infection in the lining of the womb, the bladder, episiotomy or caesarean wounds, bloodstream or lungs. Luckily, this is rare and the infection can usually be treated with antibiotics through a drip.

What problems could Group B Strep cause my baby?

In mothers who are carrying Group B Strep at the time of delivery, there is a small risk that their baby will catch the bacteria as the baby passes through the vagina. This risk depends on the gestational age (premature babies are at far higher risk), the length of time a woman’s waters have been broken and whether the woman develops a fever during labour.

A newborn baby’s immune system is less mature than that of a healthy adult. GBS can make newborn babies extremely sick. Serious GBS infections, including sepsis and meningitis, affect 1 in 1000 Australian babies.

How can I reduce the risk for my baby?

There is no way to completely eliminate the risk of Group B Strep infection for newborns. However, certain strategies can decrease the risk.

The NSW Department of Health recommends that all women be screened for GBS. This screening can be performed using either a “risk factor” checklist or by collecting a low vaginal swab at 36-37 weeks. The swab can be performed by the woman herself, which many women find more comfortable. I advise my patients to be screened using the swab.

If you have GBS on swab or you have risk factors on the checklist, you should receive antibiotics through a drip during labour. Antibiotics are proven to reduce the number of babies who develop a severe GBS infection in the first week of life.

Can I request the vaginal swab to be performed earlier in pregnancy?

It’s best to wait until 36-37 weeks. GBS in the vagina can come and go in the same patient. A vaginal swab may be negative at 24 weeks and positive at 36 weeks. It’s important to check GBS status close to delivery, so that GBS-positive women can receive appropriate antibiotic treatment in labour.

What if I go into labour before my swab is taken?

In some cases, a woman may go into labour before her vaginal swab result is available. If this happens, the woman is considered to be “GBS-unknown“. An antibiotic drip is recommended for GBS-unknown women with certain risk factors including:

  • Preterm (<37 weeks gestation)
  • Waters broken >18 hours
  • GBS in a urine test at any time during pregnancy
  • Maternal fever during labour

What if I am GBS-positive and my waters break, but I do not go into labour?

This is a fairly common situation at the end of pregnancy. 5-10% of women who are over 37 weeks pregnant will break their waters but not labour immediately. This is called pre-labour rupture of membranes.

The membranes that hold in your waters also protect your baby from infection. Once the membranes break, the risk of infection goes up significantly. If you are GBS-positive, the longer your waters are broken the more likely it is your baby will develop a serious GBS infection.

It is recommended that GBS-positive women who are over 37 weeks have their labour induced promptly after their waters break.

Breaking your waters before 37 weeks is called pre-term pre-labour rupture of membranes, or PPROM for short. PPROM is a more complicated situation.

  • If PPROM occurs before 34 weeks there is benefit in waiting for labour to start by itself. This applies as long as baby is well and there are no signs of infection in the mother. By waiting, we hope to allow extra time for the baby’s lungs to develop.
  • Between 34 and 37 weeks, the best plan will depend on a number of factors but early delivery may be of benefit in GBS-positive women. Your obstetrician will advise the best plan based on your individual circumstances.

As always, this information is intended for general educational purposes only. It is not medical advice. Please discuss any medical issues with your own doctor. Read our full medical disclaimer here.