The purpose of this study is to assess growth of preterm infants fed human milk supplemented with one of two commercially available human milk fortifiers.

Inclusion Criteria:

• Birth weight of 700 g-1500 g.
• ≤ 32 weeks and 0 days GA at birth.
• Appropriate for GA (AGA).
• Enteral feeding of human milk initiated by 21 days of life (birth date is day of life 0).
• Mother agrees to provide human milk as the exclusive feeding during the study period; use of donor milk is permitted if the plan is that it will be fortified.
• Parent(s) agrees to allow infant to receive both human milk and HMF.
• Singleton or twin births only.

Exclusion Criteria:

• Enteral feeding of preterm infant formula or HMF for > 7 days.
• Expected to be transferred to another facility and will not be able to be followed for at least 15 days.
• Serious congenital abnormalities or underlying disease that may affect growth and development.
• 5 minute APGAR ≤ 4.
• Steroids used at the time of randomization.
• Grade III or IV periventricular/intraventricular hemorrhage (PVH/IVH).
• Mechanical ventilator dependence.
• Maternal incapacity: including maternal cocaine or alcohol abuse during pregnancy or current, or if the mother or infant is currently receiving treatment consistent with HIV therapy.
• Infant has a history of major surgery (intra-thoracic or intra-abdominal procedures or other surgery requiring general anesthesia).
• Asphyxia defined as progressive hypoxemia and hypercapnia with significant metabolic acidemia characterized by APGAR score <3 at 10 minutes, seizures within the first 12 hours of life, or a cord blood gas < 7.0 and seizures and/or severe tonic abnormalities in the first 12 hours of life (24).
• Confirmed necrotizing enterocolitis (Bell's Stage II or III, Appendix J) or confirmed sepsis (positive culture requiring antibiotic treatment).
• Infant has any other condition that, in the opinion of the investigator, precludes participation in the study.
• Participation in another study that has not been approved as a concomitant study by AN.