Meghan L. Ruebel ^1,2 Stephanie P. Gilley ³ Laxmi Yeruva ^1,2 Minghua Tang ³ Daniel Frank ⁴ Ana Garces ⁵ Lester Figueroa ⁵ Renny S. Lan ^2,3 Hailemariam A. Assress ^2,6 Jennifer F. Kemp ³ Jamie L. Westcott ³ K M. Hambidge ³ Kartik Shankar ^3* Nancy F. Krebs ^3*

• ¹ Microbiome and Metabolism Research Unit, Agricultural Research Service, Agricultural Research Service, United States Department of Agriculture, Little Rock, United States
• ² Arkansas Children's Nutrition Center, Agricultural Research Service (USDA), Little Rock, Arkansas, United States
• ³ Department of Pediatrics, Section of Nutrition, University of Colorado School of Medicine, Aurora, United States
• ⁴ Division of Infectious Diseases, Department of Medicine, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
• ⁵ Instituto de Nutrición de Centro América y Panamá (INCAP), Guatemala, Guatemala
• ⁶ Department of Pediatrics, Section of Developmental Nutrition, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States

Background: Low birth weight (LBW; < 2,500g) affects approximately 15 to 20 percent of global births annually and is associated with suboptimal child development. Recent studies suggest a link between the maternal gut microbiome and poor obstetric and perinatal outcomes. The goal of this study was to examine relationships between maternal microbial taxa, fecal metabolites, and maternal anthropometry on incidence of LBW in resource-limited settings. Methods: This was a secondary analysis of the Women First trial conducted in a semi-rural region of Guatemala. Maternal weight was measured at 12 and 34 weeks (wk) of gestation. Infant anthropometry measures were collected within 48 h of delivery. Maternal fecal samples at 12 and 34 wk were used for microbiome (16S rRNA gene amplicon sequencing) and metabolomics analysis (34 wk). Linear mixed models using the MaAslin2 package were utilized to assess changes in microbiome associated with LBW. Predictive models using gradient boosted machines (XGBoost) were developed using the H2o.ai engine.Results: No differences in β-diversity were observed at either time point between mothers with LBW infants relative to normal weight (NW) infants. Simpson diversity at 12 and 34 wk was lower in mothers with LBW infants. Notable differences in genus-level abundance between LBW and NW mothers (p< 0.05) were observed at 12 weeks with increasing abundances of Barnesiella, Faecalibacterium, Sutterella, and Bacterioides. At 34 weeks, there were lower abundances of Magasphaera, Phascolarctobacterium, and Turicibacter and higher abundances of Bacteriodes, and Fusobacterium in mothers with LBW infants. Fecal metabolites related to bile acids, tryptophan metabolism and fatty acid related metabolites changed in mothers with LBW infants. Classification models to predict LBW based on maternal anthropometry and predicted microbial functions showed moderate performance.Conclusions: Collectively, the findings indicate that alterations in the maternal microbiome and metabolome were associated with LBW. Future research should target functional and predictive roles of the maternal gut microbiome in infant birth outcomes including birthweight.