Risk of Bias Across Studies
The included studies were not originally conducted with a specific focus
on GBS. However, most studies were evaluating the composition of the
microbiome across pregnancy, or related to birth outcomes that GBS can
influence, such as preterm birth (Supplementary Tables S1 andS2 ). There is notable bias against GBS reporting when only
genus level data are reported, as well as when studies only speciate
lactobacillus. For example, seven studies that did not report GBS only
assigned taxonomy to the genus level, 9 only assigned species level
assignments for Lactobacillus spp., three only assigned species
to Lactobacillus spp. and Gardnerella , and three studies
assigned taxonomy to species level, that were included in analysis, but
did not report species level results (Table S1 ). Given that
species other than lactobacillus can negatively impact vaginal health
and birth outcomes, these methods of analysis and reporting contribute
to positive bias towards Lactobacillus reporting in the vaginal
microbiome literature and negative bias towards other relevant species.
Further, four studies only reported the top 15-21 most abundant species
or taxa (Table S1 ). Since some vaginal pathogens present in low
abundance can cause pregnancy complications the underrepresentation of
these pathogens, such as GBS, may indicate bias against reporting of
microbes that are not the most abundant taxonomic groups.