The preterm placental microbiome varies in association with excess maternal gestational weight gain

Abstract

Objective: Although a higher maternal body mass index is associated with preterm birth, it is unclear whether excess gestational weight gain (GWG) or obesity drives increased risk. We and others have shown that the placenta harbors microbiota, which is significantly different among preterm births. Our aim in this study was to investigate whether the preterm placental microbiome varies by virtue of obesity or alternately by excess GWG.

Study design: Placentas (n=320) were collected from term and preterm pregnancies. Genomic DNA was extracted and subjected to metagenomic sequencing. Data were analyzed by clinical covariates that included the 2009 Institute of Medicine's GWG guideline and obesity.

Results: Analysis of 16S recombinant RNA-based metagenomics revealed no clustering of the microbiome by virtue of obesity (P=.161). Among women who spontaneously delivered preterm, there was again no clustering by obesity (P=.480), but there was significant clustering by excess GWG (P=.022). Moreover, among preterm births, detailed analysis identified microbial genera (family and genus level) and bacterial metabolic gene pathways that varied among pregnancies with excess GWG. Notably, excess GWG was associated with decreased microbial folate biosynthesis pathways and decreased butanoate metabolism (linear discriminate analysis, >3.0-fold).

Conclusion: Although there were no significant alterations in the microbiome by virtue of obesity per se, excess GWG was associated with an altered microbiome and its metabolic profile among those women who experienced a preterm birth.

Keywords: excess gestational weight gain; maternal obesity; metagenomics; microbiome; preterm birth.

FIGURE 1. Study design

The outer circle represents the numbers for 16S sequencing. The inner circle represents the numbers for whole genome shotgun sequencing, all of which also completed 16S. Of the 320 women in our original placental microbiome analysis that used 16S sequencing, 237 women had sufficiently early prenatal care to calculate GWG; of the original 48 nested whole genome shotgun cohort, 37 women had robust GWG data. GWG, gestational weight gain; WGS, whole genome shotgun. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.

FIGURE 2. Differential placental microbial abundance plots

A, The phylum-level relative abundance by body mass index, excess GWG in all subjects, and by excess GWG among preterm women. Among preterm women, there are statistically significant differences in the relative abundance of Proteobacteria, Firmicutes, Actinobacteria, and Cyanobacteria between subjects with and without excess GWG. B, Family-level relative abundance (y axis) is represented by stacked bar plots that indicate the dominant family for each of the cohorts. BMI, body mass index; GWG, gestational weight gain. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.

FIGURE 3. PCoA plots of beta diversity by body mass index

The placental microbiome does not vary with obesity. Principle coordinate analysis of all operational taxonomic units generated by 16S recombinant RNA sequencing is shown on the left. There was no significant difference in between-subject beta-diversity by virtue of obesity (permutational multivariate analysis of variance, P = .161). Among preterm placentas, the placental microbiome does not vary with obesity. Principle coordinate analysis of all operational taxonomic units generated by 16S recombinant RNA sequencing of only the preterm women is shown on the right. There was no significant difference in between-subject beta-diversity by virtue of obesity (permutational multivariate analysis of variance, P = .48). Among all women, the placental microbiome does not vary with GWG. There was no significant difference in between-subject beta-diversity by virtue of excess GWG (permutational multivariate analysis of variance, P = .186). The microbiome of preterm placentas does vary with GWG. There was statistically significant clustering by virtue of excess GWG (permutational multivariate analysis of variance, P = .022) that was most apparent along the PC1 axis (Wilcoxon rank sum, P = .02). GWG, gestational weight gain; PCoA, principal coordinate analysis; PERMANOVA, permutational multivariate analysis of variance. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.

FIGURE 4. Alpha diversity of the placental microbiome

A, Among preterm women with excess GWG, decreased species richness was observed with rarefaction alpha diversity metrics. B, Renyi alpha diversity metrics indicates varying diversity among preterm women with excess GWG. GWG, gestational weight gain. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.

FIGURE 5. Heatmap of the placental microbiome and maternal weight gain

A, Heat map demonstrates the genera relative abundance of the placental microbiome among term women without excess GWG (left), preterm subjects without excess GWG (middle) and preterm subjects with excess GWG (right). Stronger intensity of blue indicates higher relative abundance. The probability value was generated by Wilcoxon-Mann-Whitney test. Red color indicates significant difference between groups (P < .05). B, Heat map demonstrates the metabolic activity of the placental microbiome among term women without excess GWG (left), preterm women without excess GWG (middle), and preterm women with excess GWG (right). Stronger intensity of blue color indicates higher pathway activity. The probability value was generated by Wilcoxon-Mann-Whitney test. Red color indicates significant difference between groups (P < .05). GWG, gestational weight gain. P * indicates the significance of the differences between term with no excess GWG vs preterm with no excess GWG; P ** indicates the significance of the differences between preterm with no excess GWG vs preterm with excess GWG; P *** indicates the significance of the difference between term with no excess GWG vs preterm with excess GWG. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.

FIGURE 6. Metagenomics of the preterm placental microbiome by maternal weight gain

A, The Kendall correlation of metagenomics RAST server–generated Kyoto Encyclopedia of Genes and Genomes functional profile and genus level bacterial abundance were calculated and plotted. The taxa and pathways shown represent the positive (red) or negative (blue) correlations for preterm women with excess GWG. The red square indicates correlation probability value < .05. B, Among preterm placentas, excess GWG is associated with alterations in metabolic function. Detailed analysis on whole genome shotgun data show that excess GWG has decreased abundance of folate biosynthesis and butanoate metabolism. GWG, gestational weight gain; LDA, linear discriminate analysis. Antony. The preterm placental microbiome varies with excess weight gain. Am J Obstet Gynecol 2015.