Maternal Vaginal Microbiome Associated with Premature Birth

DIVERSITY of vaginal microbial flora increases risk of premature delivery. The maternal vaginal microbiome, particularly in the first trimester of pregnancy, may contribute to risk of premature birth. Higher vaginal microbial diversity, as well as the presence of specific bacteria, has been associated with increased premature birth rates.

A meta-analysis of five data sets of 415 women and >3,000 samples revealed associations between high first-trimester diversity, specific microbes, and preterm birth. “We found that women who deliver prematurely have a significantly more diverse vaginal microbiome, especially in their first trimester, than those who deliver at full term,” reported Dr Idit Kosti, first author of the study and a Postdoctoral Researcher at the Sirota laboratory, University of California San Francisco, San Francisco, California, USA.

Greater vaginal microbiome diversity has been shown in a previous study to be associated with proinflammatory genital cytokines. Previous studies highlighted that microbiome diversity was often related to different ethnic backgrounds, but the value of this meta-analysis was in the large, cross-study data sets that included an ethnically diverse cohort, and demonstrated that the impact of microbiome diversity on premature birth differed across ethnic groups.

“In addition to confirming several bacterial species known to be associated with premature birth, we have identified several new ones,” outlined Marina Sirota, an Assistant Professor at the Bakar Computational Health Sciences Institute, University of California San Francisco. Lactobacillus, identified in previous studies, was again highlighted in this meta-analysis, but newly identified, associated microbes included Olsenella and Clostridium sensu scricto.

Births before 37 weeks, considered premature delivery, are at greater risk of complications and longer-term medical problems for the newborn. Better understanding of the factors involved in premature birth may help to develop strategies to avoid early delivery, as was emphasised by Prof Sirota: “The findings could aid future diagnostic and therapeutic strategies to help prevent or delay premature birth.”

Preterm birth is the leading cause of death in newborns, and analysis of contributing factors is an important area of research scrutiny, particularly as two-thirds of preterm births are classified as ‘spontaneous’. “For most of these births, we don’t know why the women end up going into labour early and unfortunately, the limited number of therapies are often not effective,” said Prof Sirota. “New ways of identifying women at higher risk is sorely needed.”