Smaller the preterm infants at birth, more susceptible they are to iron deficiency due to low body iron stores. Despite having low iron stores, very low birth weight (VLBW) infants are not usually started on iron supplementation till they reach a postnatal age of 6 to 8 weeks. Such delayed supplementation can lead to rapid depletion of iron stores when erythropoiesis becomes active (by 8 weeks of life).