Increased richness and diversity of the vaginal microbiota and spontaneous preterm birth

Aline C Freitas,Deborah M Money,Alan Bocking,Janet E Hill

doi:10.1186/s40168-018-0502-8

Abstract

BackgroundThe bacterial community present in the female lower genital tract plays an important role in maternal and neonatal health. Imbalances in this microbiota have been associated with negative reproductive outcomes, such as spontaneous preterm birth (sPTB), but the mechanisms underlying the association between a disturbed microbiota and sPTB remain poorly understood. An intrauterine infection ascending from the vagina is thought to be an important contributor to the onset of preterm labour. Our objective was to characterize the vaginal microbiota of pregnant women who had sPTB (n = 46) and compare to those of pregnant women who delivered at term (n = 170). Vaginal swabs were collected from women at 11–16 weeks of gestational age. Microbiota profiles were created by PCR amplification and pyrosequencing of the cpn60 universal target region.ResultsProfiles clustered into seven community state types: I (Lactobacillus crispatus dominated), II (Lactobacillus gasseri dominated), III (Lactobacillus iners dominated), IVA (Gardnerella vaginalis subgroup B or mix of species), IVC (G. vaginalis subgroup A dominated), IVD (G. vaginalis subgroup C dominated) and V (Lactobacillus jensenii dominated). The microbiota of women who experienced preterm birth (< 37 weeks gestation) had higher richness and diversity and higher Mollicutes prevalence when compared to those of women who delivered at term. The two groups did not cluster according to CST, likely because CST assignment is driven in most cases by the dominance of one particular species, overwhelming the contributions of more rare taxa. In conclusion, we did not identify a specific microbial community structure that predicts sPTB, but differences in microbiota richness, diversity and Mollicutes prevalence were observed between groups.ConclusionsAlthough a causal relationship remains to be determined, our results confirm previous reports of an association between Mollicutes and sPTB and further suggest that a more diverse microbiome may be important in the pathogenesis of some cases.

Highlights

The bacterial community present in the female lower genital tract plays an important role in maternal and neonatal health
Intrauterine infection with organisms ascending from the vagina has been hypothesized as an Freitas et al Microbiome (2018) 6:117 important contributor to preterm birth since many organisms isolated from the amniotic fluid/membranes of women who experienced preterm birth are found in the lower genital tract of pregnant women [12,13,14,15]
In this study, we determined the composition of the vaginal microbiota of women who had spontaneous preterm birth and compared these profiles to those of women who delivered at term, previously reported by our research group [24]

Summary

Introduction

The bacterial community present in the female lower genital tract plays an important role in maternal and neonatal health. Imbalances in this microbiota have been associated with negative reproductive outcomes, such as spontaneous preterm birth (sPTB), but the mechanisms underlying the association between a disturbed microbiota and sPTB remain poorly understood. The ‘normal’ vaginal microbiota in non-pregnant reproductive aged women is understood to be dominated by Lactobacillus species, while an abnormal microbiota (defined as bacterial vaginosis) is characterized by low abundance of lactobacilli and an overgrowth of anaerobic bacteria, such as Gardnerella vaginalis, Prevotella spp., Bacteroides spp., Mobiluncus spp. and Mycoplasma hominis [22]. An abnormal microbiota has been previously associated with preterm birth [28], but only a few in depth culture-independent studies of the vaginal microbiota of women who had preterm birth have been published, with inconsistent conclusions [29,30,31,32]

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