Race, the Vaginal Microbiome, and Spontaneous Preterm Birth

Abstract

Previous studies have investigated the associations between the vaginal microbiome and preterm birth, with the aim of determining whether differences in community patterns meaningfully alter risk and could therefore be the target of intervention. We report on vaginal microbial analysis of a nested case-control subset of the Pregnancy, Infection, and Nutrition (PIN) Study, including 464 White women (375 term birth and 89 spontaneous preterm birth, sPTB) and 360 Black women (276 term birth and 84 sPTB). We found that the microbiome of Black women has higher alpha-diversity, higher abundance of Lactobacillus iners, and lower abundance of Lactobacillus crispatus. However, among women who douche, there were no significant differences in microbiome by race. The sPTB-associated microbiome exhibited a lower abundance of L. crispatus, while alpha diversity and L. iners were not significantly associated with sPTB. For each order of magnitude increase in the normalized relative abundance of L. crispatus, multivariable adjusted odds of sPTB decreased by approximately 20% (odds ratio, 0.81; 95% confidence interval, 0.70, 0.94). When we considered the impact of douching, associations between the microbiome and sPTB were limited to women who do not douche. We also observed strong intercorrelations between a range of maternal factors, including poverty, education, marital status, age, douching, and race, with microbiome effect sizes in the range of 1.8 to 5.2% in univariate models. Therefore, race may simply be a proxy for other socially driven factors that differentiate microbiome community structures. Future work will continue to refine reliable microbial biomarkers for preterm birth across diverse cohorts. IMPORTANCE Approximately 10% of all pregnancies in the United States end in preterm birth, and over 14% of pregnancies end in preterm birth among Black women. Knowledge on the associations between vaginal microbiome and preterm birth is important for understanding the potential cause and assessing risk of preterm birth. Our study is one of the largest studies performed to date to investigate the associations between vaginal microbiome and spontaneous preterm birth (sPTB), with stratified design for Black and White women. We found that the vaginal microbiome was different between Black and White women. The vaginal microbiome was associated with sPTB, and a lower abundance of L. crispatus increased the risk of sPTB independent of racial differences in microbial community structures. Furthermore, we also found that vaginal douching obscured the associations between vaginal microbiome, race, and preterm birth, suggesting that vaginal douching is an important factor to consider in future studies.

Keywords: douching; preterm birth; race; vaginal microbiome.

FIG 1

Associations of vaginal microbiome, race, and spontaneous preterm birth (sPTB). PCoA ordination of the vaginal microbiome colored by race (a) and term/sPTB (b). The ellipse indicates a 95% confidence limit of the centroid calculated with the function ordiellipse in R package vegan. (c) The effect sizes (R²) of host factors with PERMANOVA tests. (d) The associations between race and Shannon diversity for L. iners and L. crispatus. (e) The associations between sPTB and Shannon diversity for L. iners and L. crispatus. y axes show the Shannon diversity and log₁₀ normalized relative abundance for L. iners and L. crispatus (see Materials and Methods). Significance was determined by Wilcoxon test for Shannon diversity and ALDEx2 for L. iners and L. crispatus.

FIG 2

Vagitypes and their associations with spontaneous preterm birth. (a) The vaginal microbiome of study participants showed discrete taxonomic composition that can be classified into vagitypes. (b) The PCoA ordination of the vaginal microbiome colored by vagitypes. (c) The PCoA ordination of the vaginal microbiome colored by race and term/spontaneous preterm birth (sPTB). (d) The percentage of sPTB in each of the vagitypes. Significance was determined with Fisher’s exact test. (e) Shannon diversity of the vagitypes. The Shannon diversity of L. crispatus vagitype was significantly (P < 0.05) lower than that of L. iners vagitype, estimated with Wilcoxon test. (f) Vagitype composition of Black and White women. (g) The percentage of sPTB associated with L. crispatus and L. iners vagitypes in Black and White women. Significance was determined with Fisher’s exact test.

FIG 3

Microbial variation by race and douching and its interference with microbial signatures associated with spontaneous preterm birth (sPTB). (a) PCoA ordination colored by race and douching for samples (n = 489) with douching information available. (b) Vagitype composition of douching and nondouching Black and White women. Significance was determined with Fisher’s exact test. (c) Shannon diversity for L. crispatus and L. iners abundance by race and douching groups. The Shannon diversity for L. crispatus and L. iners abundance was significantly different for no douching White women were compared to the other three groups. Shannon diversity was analyzed with Wilcoxon test and the taxa abundance was analyzed with ALDEx2. (d) Comparison of microbial species associated with race in douching and no douching participants. The x axis is −log₁₀(P) of the associations between each taxon and race with ALDEx2 in douching group, multiplied by the direction of changes, while the y axis is in no douching group. (e) Comparison of microbial species associated with douching in Black and White participants. The x axis is −log₁₀(P) of the associations between each taxon and douching with Wilcoxon test in Black women, multiplied by the direction of changes, while the y axis describes White women. (f) PERMANOVA tests of the associations between microbiome and term/sPTB birth in each of the race and douching groups.