3. In "Study Group 1", must be able to adhere to a feeding protocol involving mother's own milk and that may include donor human milk with fortification using a human-based product (Prolact+4) or fortification with a bovine-based human milk fortifier and the use of a pre-term/term formula; or in "Study Group 2" the use of donor human milk with Prolact+4 or a pre-term/term formula from the time that the infant initiates enteral feeding through day 90 of life, until discharge from the study institution, discharge home, death or the initiation of at least 50% total oral nutrition (4 complete feeds in a 24 hour period), whichever comes first.