Vaginal Microbiome May Predict Preterm Birth

Jennifer Garcia

August 18, 2015

Composition of the vaginal microbiome may help predict preterm delivery, according to the results of a new prospective study. The results were published online August 17 in the Proceedings of the National Academy of Sciences.

The presence of a Lactobacillus-poor vaginal microbiome appeared to exhibit "both dose–response and temporal relationships with preterm birth," David A. Relman, MD, from the March of Dimes Prematurity Research Center at the Stanford University School of Medicine, California, and colleagues report.

"Further analysis of taxa abundances within [Lactobacillus-poor vaginal communities] suggested that high abundance of Gardnerella combined with low abundance of Lactobacillus might be particularly predictive of preterm birth," they add. They note that the same may be said of the presence of Ureaplasma.

The researchers conducted weekly evaluations of the microbiota of 49 women during and after pregnancy in two nonoverlapping subject groups. Both groups included term and preterm deliveries. Pregnant women were aged 18 years and older, and samples were collected from the vagina, stool, saliva, and gingiva.

Among women in the first group (n = 40), 11 delivered preterm. The authors found that there was no significant trend in microbiota diversity throughout pregnancy (P > .05, t test); however, there was substantial interindividual variability. Analysis of vaginal samples demonstrated five distinct vaginal communities, four of which were dominated by Lactobacillus spp.

Women with the fifth type, the Lactobacillus-poor vaginal microbiota, exhibited a stronger association with preterm delivery when compared with women with Lactobacillus spp. dominant vaginal flora, the researchers report. This association was present beginning early in pregnancy and persisted throughout.

The researchers also note that the duration and proportion of the time during which the vaginal flora remained Lactobacillus-poor correlated with an earlier gestational age at delivery (P = 1.1 × 10−4, Pearson; P = .015, Spearman). Gardnerella and Ureaplasma spp. were also found to be abundant in the microflora of women in this fifth category.

The investigators evaluated vaginal flora postdelivery in 25 of the 40 women and found a rapid shift in the microflora; most notably, a decline in Lactobacillus spp. and an increase in anaerobic bacteria such as Prevotella and Anaerococcus.

The researchers also evaluated an additional group of nine women during and after delivery as a validation set for three preterm risk factors identified in the first group: Lactobacillus-poor vaginal flora (<50% Lactobacillus spp.), Lactobacillus-poor vaginal flora with abundant Gardnerella, and Lactobacillus-poor vaginal flora with abundant Ureaplasma. The authors found that four women had Lactobacillus-poor vaginal flora, and two of these women delivered preterm; both of these women had abundant Ureaplasma, and one also had abundant Gardnerella.

Although the authors acknowledge that these findings are based on a relatively small number of subjects, "[o]ur findings suggest that pregnancy outcomes might be predicted by features of the microbiota early in gestation."

Funding for this study was provided by the March of Dimes Prematurity Research Center at Stanford University, National Institutes of Health National Center for Advancing Translational Science Clinical and Translational Science Award, the Stanford Child Health Research Institute, a National Institutes of Health grant, a National Science Foundation Division of Mathematical Sciences grant, and the Thomas C. and Joan M. Merigan Endowment at Stanford University. The authors have disclosed no relevant financial relationships.

Proc Natl Acad Sci. Published online August 17, 2015. Full text

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