Vaginal ‘signature’ for preterm birth in African-American women?

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A vaginal microbiome that appears to be common to African-American women who deliver preterm has been identified by researchers in a new study. Published in Nature Medicine, the data are from analysis of a subset of the National Institutes of Health Common Fund’s Human Microbiome Project (HMP).

The findings, the researchers said, hold promise for development of biomarkers that could be used to define risk of preterm birth (PTB) in this population, which has an already substantial burden of that risk. However, the results first must be replicated in other groups of African-American women in the United States.

The mission of the HMP is to characterize the human microbiota to further understanding of how the microbiome impacts human health and disease. For the current study, vaginal bacteria from 45 pregnant women who ultimately had PTB were compared with similar samples from 90 women who delivered at term. Nearly 80% of the women were African-American and the remainder were white, Hispanic, and American Indian/Alaska native.  

The researchers found lower levels of the bacterium Lactobacillus crispatus and higher levels of BVAB1, Prevotella cluster 2, and Sneathia amnii in the women with PTB. In a previous study, BVAB1, which is associated with bacterial vaginosis, and S amnii in early and mid-pregnancy were found to be associated with spontaneous PTB.

The authors then created a proof-of-concept model to identify the most discriminative taxa for PTB using data from samples collected at 24 week’s gestation or earlier. The model-which incorporate S amnii, BVAB1, Prevotella cluster 2 and TM7-H1-has an expected sensitivity of 77.4%, specificity of 76.3%, and area under the receiver operating curve of 0.723 for samples not used during training.

“Further studies are needed,” the authors concluded, “to determine whether the signatures of PTB reported in the present study replicate in other cohorts of women of African-American ancestry” and “to examine whether the observed differences in vaginal microbiome composition between women of different ancestries has a direct causal link to the ethic and racial disparities in PTB rates.”