BACKGROUND Children prenatally exposed to inadequate iron have poorer motor and neurocognitive development. No prior study to our knowledge has assessed the influence of maternal prenatal iron intake on newborn brain tissue organization in full-term infants. METHODS Third trimester daily iron intake was obtained using the Automated Self-Administered 24-h Dietary Recall with n = 40 healthy pregnant adolescents (aged 14-19 y). Cord blood ferritin was collected in a subsample (n = 16). Newborn (mean = 39 gestational weeks at birth; range 37-41) magnetic resonance imaging scans were acquired on a 3.0 Tesla MR Scanner. Diffusion Tensor Imaging (DTI) slices were acquired to measure the directional diffusion of water indexed by fractional anisotropy (FA). RESULTS Reported iron intake was inversely associated with newborn FA values (P ≤ 0.0001) predominantly in cortical gray matter. FA findings were similar using cord blood ferritin values. CONCLUSIONS Higher maternal prenatal iron intake accentuates, and lower intake attenuates, the normal age-related decline in FA values in gray matter, perhaps representing increasing dendritic arborization and synapse formation with higher iron intake. These DTI results suggest that typical variation in maternal iron outside the scope of standard clinical surveillance exerts subtle effects on infant brain development.