Background: Effects of prenatal iron supplementation on maternal postpartum iron status and early infant iron homeostasis remain largely unknown. Objective: We examined iron absorption and growth in exclusively breastfed infants in relation to fetal iron exposure and iron status during early infancy. Design: Longitudinal, paired iron-absorption (<58<Fe) studies wereconducted in 59 exclusively breastfedPeruvian infants at 2-3 mo of age (2M) and 5-6 mo of age (5M). Infants were born to women who received ≥5100 or ≤1320 mg supplemental prenatal Fe. Iron status was assessed in mothers and infants at 2M and 5M. Results: Infant iron absorption from breast milk averaged 7.1% and 13.9% at 2M and 5M. Maternal iron status (at 2M) predicted infant iron deficiency (ID) at 5M. Although no infants were iron deficient at 2M, 28.6% of infants had depleted iron stores (ferritin concentration <12 μg/L) by 5M. Infant serum ferritin decreased (P < 0.0001), serum transferrin receptor (sTfR) increased (P < 0.0001), and serum iron decreased from 2M to 5M (P < 0.01).Higher infant sTfR (P < 0.01) and breast-milk copper (P < 0.01) predicted increased iron absorption at 5M. Prenatal iron supplementationhad no effects on infant iron status or breast-milk nutrient concentrations at 2M or 5M. However, fetal iron exposure predictedincreased infant length at 2M (P < 0.01) and 5M (P < 0.05). Conclusions: Fetal iron exposure affected early infant growth but did not significantly improve iron status or absorption. Young, exclusivelybreastfed infants upregulated iron absorption when ironstores were depleted at both 2M and 5M. © 2013 American Society for Nutrition.