Year: 2018
Type: article
Abstract: It seems logical that the composition of the vaginal microbiota would be a significant variable influencing pregnancy outcome. Bacteria that are not part of the normal microbiota can trigger induction of myometrial contractions and premature delivery. Components of the endogenous microbiome may also be capable, under conditions that are still ill-defined, of interfering with pregnancy progression. A recent PubMed search identified 99 publications under the heading, ‘vaginal microbiome in pregnant women’. Conclusions from these multiple studies vary widely, ranging from no influence of the microbiome on outcome to identification of associations between specific bacteria or groups of bacteria, or the absence of specific bacterial species, and preterm delivery (Romero et al. Microbiome 2014;2:18; Callahan et al. Proc Natl Acad Sci USA 2017;114:9966). When present, associations between specific bacteria (or their absence) and outcome have been relatively small. The study by Tabatabaei et al (BJOG 2019;126:349–58) now reports that the predominance of any of four different bacteria in the vagina, Lactobacillus gasseri/ Lactobacillus johnsonii, Lactobacillus crispatus/ Lactobacillus acidophilus, Lactobacillus iners/Ralstonia solanacearum or Bifidobacterium longum/Bifidobacterium breve, is associated with a decreased risk of preterm birth before 34 weeks of gestation. The method of bacterial detection, sequencing of the V4 region coding for 16S ribosomal RNA, did not allow for a more precise differentiation of bacterial species. A shortcoming of almost all vaginal microbiome–pregnancy studies, and a likely reason for the variable conclusions, is the absence of a concurrent analysis of host factors. Clearly, variations (polymorphisms) in genes that influence the direction and magnitude of the immune response to specific stimuli as well as the extent of a stress response to various situations will differ between women (Ramos et al. Am J Reprod Immunol 2015;73:383–9; Sisti et al. Genes Immun 2016;17:1–7). Metabolic or dietary differences or frequency of sexual activity, douching, or use of vaginal hygiene products alter the composition of vaginal secretions. The concurrent presence of an asymptomatic viral, protozoal or fungal infection modifies the host response to vaginal bacteria. The extent by which these factors influence the composition of the vaginal microbiome and, perhaps more importantly, their effect on the magnitude of host responses to specific bacteria or groups of bacteria will vary greatly between individual women. It is short-sighted to assume that all women will have a uniform response to the same bacteria and that their local environments are identical. Hence, characterisation in isolation of the vaginal microbiome in healthy asymptomatic pregnant women in the absence of a concurrent thorough evaluation of differences in host factors will provide only an incomplete picture of microbiome–pregnancy interactions. The ability to recognise situations where the presence or absence of specific bacteria may interfere with pregnancy progression awaits a more thorough analysis and understanding of bacteria–host interactions. None declared. Completed disclosure of interests form available to view online as supporting information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Author: SS Witkin
Institution: Weill Cornell Medicine
Language: English
Subfield: Microbiology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2803472496