Group B Strep in Pregnancy

Group B streptococcus (GBS) is a normal part of the vaginal microbiome, but becomes a common concern usually in the third trimester of pregnancy if there is an overgrowth of the bacteria. Roughly 10 to 35% of pregnant women are colonized with GBS in various areas of their body including the vagina and rectum. Around 36 weeks of pregnancy, GBS colonization is about 19.5%.

Because GBS is part of the normal vaginal microbiome, most pregnant people don’t experience any GBS symptoms. However, it can result in rare symptoms such as urinary tract infections, amnionitis, endometritis, sepsis and meningitis. Transmission to baby may happen during delivery, if the infection crosses intact membranes, or if GBS is spread into the amniotic fluid and then aspirated. Unfortunately this can result in stillbirth, or bacteremia, pneumonia, or meningitis.

Risk factors for GBS include

  • Ethnicity
  • Maternal age
  • Martial status
  • Education
  • Smoking
  • Multiple sexual partners


Screening Guidelines

Between 35-37 weeks a vaginal-rectal swab is taken in pregnant people to determine GBS colonization. Re-screening may occur if more than 5 weeks have passed from the initial swab, and birth has yet to happen. However, according to SOGC guidelines, if you have been colonized with GBS (at any time during your pregnancy), re-screening is recommended and you’re considered GBS positive.


Standard Treatment

If GBS is present (GBS positive), antibiotics will administered at time of labour, preterm labour (less than 37 weeks), prolonged rupture of the membranes (over 18 hours), maternal fever (equal to or over 380C). In addition if you have a child with previous GBS infection then you will be administered antibiotics.

If you are GBS positive and are not treated with antibiotics, your baby’s risk of developing an infection is 1% to 2%, and if you are treated with antibiotics the risk drops to about 0.2%.


Preventing GBS

In 2016, a study determined the effect of probiotics on the vaginal flora of GBS positive women. In pregnant women between 35 to 37 weeks, 99 were diagnosed as GBS positive. These women were divided into two groups – probiotics and placebo.

The probiotic group took 2 oral probiotics capsules (with L. rhamnosus GR-1 and L. reuteri RC-14) prior to bed until their delivery date, and the placebo group took 2 placebos before bed until their delivery date.

At their delivery date another swab was administered to assess if they were still GBS positive. In the probiotic group, 42.9% in women were now GBS negative, while in the placebo group, only 18% were GBS negative.

Because GBS re-testing is not routine, adding a probiotic to your daily routine starting early in pregnancy may be a worthwhile endeavour. Especially if you are at risk of being GBS positive due to a history of UTIs and bladder infections or were GBS positive during a previous pregnancy.



Association Of Ontario Midwives: Group B Streptococcus Prevention And Management In Labour (January 2010). Retrieved from:

Dekker R. The Evidence on: Group B Strep. (2017). Retrieved from:

Ho M, Chang Y, Chang W et al. Oral Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 to reduce Group B Streptococcus colonization in pregnant women: A randomized controlled trial. Taiwanese Journal of Obstetrics and Gynecology. 2016;55(4):515-518. doi:10.1016/j.tjog.2016.06.003.

SOGC: Management of Group B Streptococcal Bacteriuria in Pregnancy (2012). Retrieved from:


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