Large-scale characterisation of the pregnancy vaginal microbiome and sialidase activity in a low-risk Chinese population

Vaginal microbiota-host interactions are linked to preterm birth (PTB), which continues to be the primary cause of global childhood mortality. Despite the majority of PTB occuring in Asia, studies of the pregnancy vaginal microbiota are largely limited to Northern American and European populations. Here, we characterised the vaginal microbiome of 2689 pregnant Chinese women using metataxonomics and in a subset (n=823), the relationship between vaginal microbiota composition, sialidase activity and leukocyte presence and pregnancy outcomes. Vaginal microbiota were most frequently dominated by Lactobacillus crispatus or L. iners , with the latter associated with vaginal leukocyte presence. Women with high sialidase activity were enriched for bacterial vaginosis-associated genera including Gardnerella, Atopobium and Prevotella . Vaginal microbiota composition, high sialidase activity and/or leukocyte presence was not associated with PTB risk suggesting underlying differences in the vaginal microbiota and/or host immune responses of Chinese women, possibly accounting for low PTB rates in this population. Importance Specific vaginal microorganisms or ‘vaginal microbiota’, are associated with preterm birth, which is the primary cause of death in children under 5yrs of age worldwide. Despite most preterm births occuring in Asia, almost all studies of the pregnancy vaginal microbiota have been limited to Northern American and European women. Here, we studied the vaginal microbiota in a large cohort of 2689 pregnant Chinese women and showed that it was most frequently dominated by Lactobacillus crispatus or L. iners . The latter was associated with leukocyte infiltration of vaginal secretions. Women with high activity of the enzyme sialidase, were frequently colonised by species associated with the common condition bacterial vaginosis, including Gardnerella, Atopobium and Prevotella species. Vaginal microbiota, high sialidase activity and/or leukocyte presence was not associated with preterm birth risk indicating differences in the microbe-host immune responses of Chinese women, possibly explaining why preterm birth rates in this population are low.