A longitudinal study of 1,074 mother-child pairs reveals that DHA-carrying phosphatidylethanolamine plasmalogens (PEP-DHA) — specialized phospholipids distinct from standard DHA — serve as crucial mediators between early nutrition and infant neurodevelopment. Higher PEP-DHA levels in both maternal and infant blood were associated with improved cognitive and language outcomes at age two years. The research demonstrates that prenatal diet quality influences infant cognition partly through maternal PEP-DHA levels, while the cognitive benefits of breastfeeding are substantially mediated by infant PEP-DHA levels at six months. This finding advances our understanding beyond simple omega-3 supplementation, suggesting that the structural form of DHA matters significantly for brain development. Plasmalogens are particularly abundant in brain tissue and serve specialized roles in membrane function and neuroprotection. The research implies that optimizing maternal diet quality and promoting breastfeeding may enhance specific lipid pathways critical for infant brain development. However, as this medRxiv preprint awaits peer review, these mechanistic insights require validation. The findings could inform more targeted nutritional strategies for supporting optimal neurodevelopment, potentially shifting focus from total DHA intake to specific phospholipid forms that maximize brain benefits.