Research question: Do preterm infants born \<1250 g achieve better weight gain with targeted fortification compared with the adjustable fortification of human milk? Hypothesis: Targeted fortification of human milk results in better weight gain in infants with birth weight \<1250 gr when compared to the adjustable fortification. Study design: Open-label, pragmatic, parallel randomized controlled trial in appropriate for gestational age infants with birth weight \<1250 g.