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Pathologic states (obesity) and physiologic states (pregnancy) are accompanied by changes in the microbiome. Unique to pregnancy is a physiologic state of increasing adiposity, although this can cross-over to pathologic if weight gain is excessive. Our aim was to investigate whether excess gestational weight gain affects the microbiome in pregnancy and, if so, the biologic significance.
Placentas (n=243) were rigorously and uniformly collected from term and preterm gravidae and stratified by IOM GWG guidelines. Genomic DNA was extracted (MoBIO), and metagenomic libraries (n=26) were subjected to shotgun sequencing (WGS; Illumina).
16S rRNA pyrosequencing (1A) revealed no significant difference in between-subject beta-diversity by virtue of obesity (p=0.22), nor excess GWG (p=0.189). However, among gravidae with preterm births, there was significant clustering by excess GWG (p=0.022), and species richness (abundance across multiple taxa) was notably decreased. Among all gravidae, detailed analysis of WGS with linear discriminant analysis (LDA) identified microbial genus that were significantly differentially abundant among placentas from gravidae with excess GWG (1B.) This detailed analysis also uncovered significant differences in the metabolic function; excess GWG associated with decreased activity of placental microbial folate biosynthesis pathways and decreased butanoate metabolism (1C).
Overall, while there were no alterations in the microbiome by virtue of obesity, excess weight gain did alter the microbiome among those with preterm birth. Deeper metagenomic sequencing revealed excess GWG was associated with alterations in the abundance of certain genuses and functional pathways in the placental microbiome. Some of these pathways may affect the inflammatory milieu; for example, butanoate is posited to suppress colonic inflammation in the gut. We speculate that these alterations may contribute to increased morbidity among gravidae with excess gain.