Fig. 2

Identifying differential species between groups with recurrence and those without recurrence. A Principal coordinate analysis (PCoA) plot of beta diversity based on robust Aitchison distance for the preterm and term birth groups in the early and late stages of pregnancy with p-values determined by analysis of similarities (Adonis2). B Beeswarm boxplot of alpha diversity values (Observed, Chao1, Shannon, Simpson) by outcome in early and late pregnancy, with line and whiskers representing the median and inter-quartile range, respectively. C Random forest plots highlighting the top 15 microbial biomarkers distinguishing the preterm group from the term group. Species were ranked in descending order of their importance according to the mean decrease in their Gini score. (D) Linear discriminant analysis (LDA) score determined by the LDA effect size (LEfSe) analysis showing biomarkers between the preterm and term group. The threshold for LDA score was > 2 in early pregnancy and > 4 in late pregnancy. The letter before the taxa indicates taxonomic level: “p__” for phylum; “c__” for class; “o__” for order; “f__” for family; “g__” for genus; and “s__” for species. E Box plots comparing the relative abundance of Lactobacillus crispatus and Lactobacillus iners by pregnancy outcome in early and late pregnancy. F Bacterial co-occurrence networks (SparCC correlation, the most abundant 25 species, p value < 0.05, and correlation > 0.1). The node represents bacterial species. The size of a node is proportional to its abundance. The edge color represents positive (green) and negative (red) correlations, and the edge thickness is equivalent to the correlation value. Statistical significance is shown as \(^{*}\)P value < 0.05, \(^{**}\)P value < 0.01, \(^{***}\)P value < 0.001