A prospective study in Human Reproduction found that women with recurrent miscarriage showed consistently elevated metabolites in the NAD Salvage Pathway across plasma, blood, and urine. Among 88 non-pregnant women, those with two or more miscarriages had markedly higher plasma 1-methylnicotinamide (151 vs 89 nM), 2PY, and 4PY. Each unit rise in 1MNA increased miscarriage odds by 2%, independent of age. Spot urine reliably reflected metabolic alterations. Machine-learning models integrating 1MNA, 2PY, 4PY, and age reached an AUROC of 0.889. Findings suggest heightened NAD consumption or methylation activity, potentially tied to inflammation or metabolic dysregulation.