Probiotics for GBS: What do studies show?

This is a guest post from Krystina Friedlander, student midwife at the Concord Birth Center. Her website is

In the Boston and New Hampshire home birth midwifery community, we typically recommend oral probiotics in the weeks leading up to the 36-week Group B Streptococcus (GBS) test (which, FYI, some parents opt out of). Here, I dig into what recent research shows about the effectiveness of using probiotics to regulate GBS. For more on GBS, I recommend reading the Evidence Based Birth article. For more reading on the role that healthy bacteria plays in your body and how it relates to childbirth, read this blog postPlease let me know if there is research that I haven’t included here!

A number of studies indicate that the use of probiotics may be helpful in reducing GBS colonization in late pregnancy, which reduces the risk of GBS infection in newborns (which, though rare, is very dangerous).

While small studies show a benefit, we’re still waiting on a really big randomized control trial to make a very strong case.

Some questions that continue to arise for me:

  • Should we take probiotics throughout pregnancy, beginning in the first trimester, or target it to specific weeks of pregnancy?
  • If we should take them prior to the 36-week mark (when GBS testing is performed), how many weeks prior is early enough to be effective?
  • What specific strains, in what specific amounts, and in what specific dosages?
  • Oral or vaginal? Are they equal? How does an oral probiotic change vaginal flora?
  • Are there dietary changes (more fermented foods, less refined sugar, etc) that can have supportive effects on vaginal lactobacilli populations?
  • Do probiotics make up for a poor diet? Can they?

Should everyone take probiotics in pregnancy, or just people who are GBS+?

In short, yes, evidence supports the use of probiotics to control GBS colonization. But what if you test negative at 36 weeks?

While most women who test negative for GBS at 36 weeks will remain so at 40 weeks, one study showed that 61% of GBS infections occurred in babies whose mothers tested negative but then were positive by 40 weeks. This doesn’t mean that we need to institute universal antibiotics for people in labor–remember, GBS overall is rare, and the universal approach is questionable–rather, it should call for the judicious use of antibiotics when risk factors are at play. It also suggests that lactobacilli probiotics would be useful among even those who test negative for GBS in anticipation of their labors.

Because there are no risks associated with taking oral probiotics in pregnancy, and because there are potential benefits to it, my belief (and that of the midwives in my community) is that everyone can benefit from supporting their gut and vaginal microbiome in pregnancy, and at any point in pregnancy. Because the cost of quality probiotics can be high, I would recommend adding fermented foods such as daily kimchi, sauerkraut, and sugar-free, whole milk yoghurt to the diet, and/or taking a good probiotic beginning around 31-32 weeks of pregnancy.

Other interesting studies I came across…

  • According to this 2013 study in Acta Pediatrica, the use of antibiotics in labor decreased the transmission of healthy vaginal lactobacilli to the baby at birth. If we agree that healthy gut seeding is important for infants, then this supports the “risk based approach” to GBS (UK standard of care) as opposed to universal use of antibiotics in labor (US standard of care).
  • The ongoing Probiotics in Pregnancy (PiP) Study in New Zealand examines whether probiotic supplementation in pregnancy and while breastfeeding can improve long term allergy and eczema in infants.
  • Not about GBS, but this study from the Pakistan Journal of Medical Sciencesfound that infant probiotics helped to resolve neonatal jaundice.
  • Ronnie Falcao has a list of studies relating the microbiome to various aspects of infant health.
Krystina Friedlander