Vaginal Microbiome Predicts Risk of Premature Labor

The composition of a woman's vaginal microbial community may predict risk of preterm birth. According to a study published Aug. 17 in Proceedings of the National Academy of Sciences a specific bacterial pattern ups the risk of preterm delivery, and the longer the pattern persists, the greater the risk. The authors say the findings have important implications for pregnancy outcomes.

Preterm birth is a sizable problem globally. In the United States alone there are approximately 450,000 babies born prematurely each year. Prior research suggests that at least a quarter of preterm births are associated with occult microbial invasion of the amniotic cavity, most often from the mother's host microbiota. Given this link, the researchers analyzed the microbiomes of 49 pregnant women, 15 of whom delivered preterm. From 40 of these women (in the discovery cohort) the researchers analyzed the microbiota from 3,767 specimens (collected prospectively and weekly during gestation and monthly after delivery from the vagina, distal gut, saliva, and tooth/gum) to characterize temporal changes and community features associated with preterm birth. For the nine women in the validation set, 246 vaginal samples were analyzed.

The researchers found that microbiota community composition remained "remarkably" stable at all four body sites during pregnancy. A distinct vaginal community pattern dominated by a low prevalence of Lactobacillus bacteria with elevated abundances of Gardnerella or Ureaplasma (community state type [CST] 4) was significantly associated with preterm delivery. This finding was similarly seen in the validation cohort in which four of the nine women delivered preterm.

"Of note, if we had collected specimens less frequently than weekly, we would have missed a number of excursions to CST 4 and hence would have been hindered in associating this state with preterm birth," write the authors. The authors also observed that most women experienced a post-delivery disturbance in the vaginal community characterized by a decrease in Lactobacillus species and an increase in diverse anaerobes species, which persisted for up to one year post delivery. While this disturbance was unrelated to gestational age at delivery, the authors say it may have implications for the known increased risk for preterm birth in women whose pregnancies are closely spaced.

"Our data suggest that if the microbiome plays a role in premature birth, it may be something that is long in the making," lead author, Daniel DiGiulio, M.D., Stanford University (California), said in a statement. "It may be that an event in the first trimester or early second trimester, or even prior to pregnancy, starts the clock ticking.... We now recognize that our bodies' microbial communities perform many beneficial functions, yet there may be times when the communities get out of whack."

Takeaway: While the findings need further validation in a larger, more diverse group of women, in the future, testing the vaginal microbiome may identify which women are at risk for premature delivery, which may ultimately be preventable through early intervention with a probiotic treatment.