The prevention of postnatal growth failure in very low birth weight (VLBW) preterm infants is of utmost importance. Fortified human milk is the goal for preterm infants' nutrition. Standard fortification is the most commonly used and safe supplementation practice but it does not consider the native variability of human milk. Data on efficacy and safety of prolonged target fortification are scarce. Prospective interventional study was conducted in VLBW preterm infants, exclusively fed with human milk. Twenty-four hour collected pools of human milk were analyzed and targeted human milk fortification was performed during hospitalization. Weekly growth and daily growth velocity were compared with that of an historical group of VLBW preterm infants that had received standard fortified human milk. Osmolality, metabolic and gastrointestinal tolerance were monitored.