Non-linear and non-additive associations between the pregnancy metabolome and birthweight

•We identified the association between 46 metabolites and birthweight z-score.•All 46 metabolites showed evidence of U-shape associations with birthweight z-score.•85% the identified metabolites were lipids, showing synergistic relationships.•Metabolites were enriched for pathways vital for pregnancy-parturition processes.•The MWAS analysis identified only 3 metabolites associated with birthweight z-score.