Systematic review finds oral probiotics decrease GBS colonization in pregnant people with variability

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medRxiv Published May 3, 2026 Medically reviewed May 3, 2026 Study authors: Raskin, D. M.; Rowland, K.; Broughton, A. DOI ↗ By Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

Key Takeaway

Note variability in probiotic effects on GBS colonization; more studies needed before routine use.

This systematic review and meta-analysis examined the impact of oral probiotic administration on Group B Streptococcus colonization in pregnant individuals. The analysis included data from 14 randomized controlled clinical trials comparing probiotic use against placebo or control groups. The primary outcome assessed was the rate of GBS colonization.

The pooled results indicated a statistically significant decrease in GBS colonization rates among those receiving probiotics. Despite this overall positive trend, the authors noted that individual studies showed great variability in their outcomes. This inconsistency limits the ability to draw definitive conclusions about the uniform effectiveness of the intervention across different settings.

Safety data were not reported, including information on adverse events, serious adverse events, discontinuations, or tolerability. The authors acknowledge that more studies need to be performed to use probiotics effectively and decrease antibiotic usage. Until further research resolves the observed variability, the clinical application of this strategy remains uncertain.

Study Details

Study typeMeta analysis

EvidenceLevel 1

PublishedMay 2026

View Original Abstract ↓

Abstract: Background: Transfer of Streptococcus agalactiae, or Group B Streptococcus (GBS) from parent to newborn during delivery can produce life-threatening infections in neonates. Probiotics could potentially prevent GBS colonization in pregnant individuals. We conducted a systematic review and meta-analysis to evaluate the effectiveness of probiotic administration in treating Group B Streptococcus colonization. Methods: MEDLINE, ClinicalTrials.gov, PROSPERO, and the Cochrane, Wild Card, Central Register of Controlled Trials were searched from the July 2015 of each database until July 2025 that completed a randomized controlled trial which compared Probiotic versus control. We utilized the Cochrane Risk of Bias 2.0 (RoB 2) tool to assess bias in the systematic review. Results: 14 randomized controlled clinical trials met our inclusion criteria. The trials used oral probiotic administration compared to either a placebo or a control group. A meta-analysis showed that probiotic administration produced a statistically significant decrease in the rate of GBS colonization in pregnant individuals. The individual studies ranged from four showing great effectiveness, while the other 10 studies showed a range of effectiveness, from partially effective to no effectiveness in preventing GBS colonization. Conclusion: Overall, probiotics were effective in lowering infection rates of GBS, but individual studies showed great variability. Probiotics show promise in decreasing GBS colonization in pregnant people, but more studies need to be performed in order to use them effectively and decrease antibiotic usage.