Gut Microbiota Composition in Mid-Pregnancy Is Associated with Gestational Weight Gain but Not Prepregnancy Body Mass Index

Background: Pregnancy is a time of numerous hormonal, metabolic, and immunological changes for both the mother and the fetus. Furthermore, maternal gut microbiota composition (GMC) is altered during pregnancy. One major factor affecting GMC in pregnant and nonpregnant populations is obesity. The aim was to analyze associations between maternal overweight/obesity, as well as gestational weight gain (GWG) and GMC. Moreover, the modifying effect of depression and anxiety symptom scores on weight and GMC were investigated. Methods: Study included 46 women from the FinnBrain Birth Cohort study, of which 36 were normal weight, and 11 overweight or obese according to their prepregnancy body mass index (BMI). Stool samples were collected in gestational week 24, and the GMC was sequenced with Illumina MiSeq approach. Hierarchical clustering was executed to illuminate group formation according to the GMC. The population was divided according to Firmicutes and Bacteroidetes dominance. Symptoms of depression, general anxiety, and pregnancy-related anxiety were measured by using standardized questionnaires. Results: Excessive GWG was associated with distinct GMC in mid-pregnancy as measured by hierarchical clustering and grouping according to Firmicutes or Bacteroidetes dominance, with Bacteroidetes being prominent and Firmicutes being less prominent in the GMC among those with increased GWG. Reduced alpha diversity was observed among the Bacteroidetes-dominated subjects. There were no zero-order effects between the abundances of bacterial genera or phyla, alpha or beta diversity, and prepregnancy BMI or GWG. Conclusion: Bacteroidetes-dominated GMC in mid-pregnancy is associated with increased GWG and reduced alpha diversity.