The goal of this study is to evaluate the short-term effect (up to 90 days of life) of purely human-based nutrition using mother's own milk (when available), donor milk preparations and a human-based fortifier (Prolact+4) as needed when compared with mother's own milk supplemented with pre-term formula and using a bovine-based HMF (as needed for fortification of mother's own milk), i.e. "Study Group 1"; or, when mother's milk is not available, comparing the use of donor milk (plus human milk based fortification) with pre-term/term formula, i.e. "Study Group 2". In both instances the comparison will be based on the primary endpoint of days of TPN, and on parameters such as time to full enteral feeding (approximately 150-160 mL/kg/day), amount of IV fluid support, culture-proven sepsis, NEC, death, growth and short-term development, cultured-proven sepsis and incidence of feeding intolerance in either a 2-arm (human nutrition versus bovine nutrition: "Study Group 2") or 3-arm randomized design (human fortifier given when feedings reach 40 mL/kg/day, human fortifier given when feedings reach 100 mL/kg/day, and bovine-based HMF given when feedings reach 100 mL/kg/day [or pre-term formula if mother's milk is not available]: "Study Group 1").