Correlations Between Threatenedpreterm Birth And Microbial Communities During Pregnancy

BackgroundPreterm birth is the most common cause of death in perinatal infants and children under 5 years old,placing a heavy burden on families and public health care system.Thanks to the progressing of neonatal intensive care unit recently,parents have positively shifted their attitudes towards saving of premature infants less than 28 weeks of gestation.Increasing attention has been paying to extremely preterm birth.Existing hypotheses including infection/inflammation,uterine overdistention,maternal-fetal HPA axis activation,psychological factors,cervical diseases,vascular disorders and breakdown of maternal-fetal tolerance,have failed to elucidate the underlying pathogenesis of preterm birth.Furthermore,due to the lack of specific precursory symptoms,there has been as yet no effective precautions for such disease.There has always been a wide and comprehensive interaction between microbiome and the host,which together constitute a steady micro-ecosystem in human body.Microbiome can be easily affected by multiple factors like ethnics,age and so on.Series of physiological changes occur systematically during pregnancy,so as the microbiome.However,imbalances of microbial ecology may induce metabolic disorders,immune intolerance,initiation of focal or systemic inflammatory responses which further contribute to complications of pregnancy such as gestational diabetes,preeclampsia,premature birth,thereby affecting short-and long-term prognosis of perinatal babies.With the development and prevalence of 16S rRNA sequencing technology,people have gradually realized the correlations between maternal periodontal disease,vaginal flora and adverse pregnancy outcomes.However,there are still few studies on the correlation between oral/intestinal microbiome structure and extremely preterm birth in Chinese population.And whether the oral,vaginal and intestinal microbiota of mother are involved synergistically in the incidence of threatened preterm labor needs further study.ObjectivesIn this study,we aim to preliminary explore the correlation between threatened preterm labor and the oral,vaginal,intestinal microbial community structures of women.Try to analyze the etiology of threatened preterm birth from the perspective of microorganisms and provide a theoretical basis for further research.MethodsStudy has been conducted on extremely preterm birth in 24+0-27+6 weeks,according to the guideline of ACOG for preterm birth.Women who underwent routine prenatal examinations in obstetric outpatient clinic and patients that hospitalized for symptoms including regular or irregular uterine contractions accompanied by a change in cervical effacement and cervical dilation less than 2 cm in Nanfang Hospital of Southern Medical University from December 2018 to September 2019 have been recruited and divided into as health group and preterm group separately.Prenatal and medical history,oral swabs,vaginal secretions and fecal specimens were collected.For preterm group,patients were further classified into two subgroups called PLT and Threatened PLT according to whether they have gone through preterm labor or not.Total DNA of oral,vaginal and intestinal microbiome from preterm and health groups were extracted.Then amplified the bacterial 16S rDNA V4 genes region followed by Illumina sequencing.Bioinformatic analysis and statistical processing were performed to explore flora characteristics of oral,vaginal and intestinal microbiome during pregnancy in two groups.Results1.Analysis of oral flora results:Compared with the health group,the alpha diversity of oral flora in the preterm group had decreased,but the difference was not statistically significant.Beta-diversity of oral floras in preterm group were significantly different from that in health group.In addition,at the genus level,Gardnerella,Lactobacillus,Atopobium and Aggregatibacter were enriched in oral flora of health group.The dominant floras in preterm group were Faecalibacterium,Bacteroides and Granulicatella.2.Analysis of vaginal flora results:The vaginal flora in preterm group had higher alpha-diversity indices than those in health group without statistical difference.The dominant floras of vagina in both groups were Lactobacillus.The proportion of Lactobacillus in health group was higher than that in health group(43.52%vs 46.01%).After that,it was followed by Streptococcaceae_genus,Gardnerella,Bifidobacterium in sequence.The results of PCoA analysis of vaginal flora showed that the microbial composition of each sample within the same group was similar to one another,which means that the vaginal floras in preterm group were significantly different from those in health group(P<0.05).LEfSe analysis showed that there were 15 kinds of flora with significant differences in the two groups.Among them,Atopobium,Aerococcus and Aerococcaceae were enriched in the health group,while Clostridiales,Clostridia,Gammaproteobacteria,Enterobacteriaceae,Enterobacteriales and other seven species were enriched in preterm group.3.Analysis of intestinal flora results:The alpha-diversity indices of intestinal flora were decreased in preterm group.Beta-diversity analysis showed no significant difference in the composition of intestinal flora between the two groups.Compared with the health group,the abundance of Firmicutes was increased(77.78%vs 71.17%),whereas Proteobacteria(6.82%vs 12.66%),Actinobacteria(7.83%vs 12.10%),Bacteroidetes(2.03%vs 2.89%)were decreased in the preterm group.The ratio of Bacteroidetes/Firmicutes was decreased.LEfSe analysis showed that Lachnospira,Erysipelotrichi,Erysipelotrichales and Erysipelotrichaceae were enriched in preterm group.There was no dominant flora enriched in health group.Conclusions1.Compared with the health group,the oral flora composition of the preterm group is markedly different.The opportunistic pathogens,particularly Granulicatella,were enriched in the preterm group,while the beneficial bacteria such as Lactobacillus and Bifidobacterium were enriched in the health group2.The composition of vaginal flora in the threatened preterm patients were significantly different from that in healthy pregnant women.In the preterm group,the relative abundance of Lactobacillus decreased whereas pathogenic bacteria such as Enterobacteriaceae and Gamma-proteobacteria were enriched.3.The composition of intestinal microbial community between the threatened preterm patients and healthy pregnant women was not markedly different.However,compared with the health group,the abundance of Firmicutes was increased,while Proteobacteria,Actinobacteria,Bacteroidetes were decreased in the preterm group.The ratio of B/F was decreased.The abundance of the genera of Ruminococcaceae(short-chain fatty acid-producing bacteria)has decreased in preterm group.Although there was no dominant flora enriched in health group,Lachnospira,Erysipelotrichi were enriched in preterm group.