Vaginal microbial community and risk of pre-term birth: an ecological perspective

Background/Question/Methods

Accurately predicting and preventing preterm birth remains a challenge to the medical community: nearly 12% of all deliveries occur at <37 weeks. Intrauterine infection accounts for 25-40% of preterm births, but previous medical studies clearly suggest there is not a single pathogen-disease causal relationship in preterm birth. An ecological study is needed to answer (1) whether host biological and behavioral traits and (2) whether inter-specific interactions within the vaginal pathogenic and commensal bacteria community contribute to the risk of preterm birth.

We used q-PCR to examine targeted reproductive pathogenic and commensal bacteria from vaginal microbial samples taken from 354 pregnant women with previous preterm birth experience. We then used ecological community analysis techniques to investigate the correlation between microbial community structure, host characteristics and preterm birth risk of the current pregnancy. 

Results/Conclusions

We found a significant correlation between the bacterial community structure and birth outcome, but the correlation differed among racial/ethnic groups. We observed infrequent co-occurrence of Mycoplasma and Bacteria Vaginosis Associated Bacteria 3 (BVAB3) among black and Hispanic participants.  In these two ethnic groups, we also found a positive correlation between Mycoplasma and preterm birth, as well as a protective effect of BVAB3 in black participants. In addition, we found that the vaginal bacterial community responded differently in different ethnic groups to modifications of maternal behavioral (i.e., douching and smoking) and biological traits (i.e. BMI). Even after accounting for these maternal traits, the microbial community was still significantly associated with preterm birth among black and Hispanic participants.  By contrast, white participants' maternal traits and behaviors largely accounted for the correlation between the vaginal bacteria and preterm birth, suggesting maternal traits explain microbially-mediated preterm birth. Findings from this study affirm the necessity of considering women’s ethnicity when evaluating the correlation between vaginal microbiota and preterm birth. The study also illustrated the importance of studying the vaginal microbiota from an ecological perspective, and demonstrated the power of ecological community analysis to improve understanding of infectious disease.