Preterm and very low birth weight (VLBW, \< 1,500g) infants who receive donor human milk (DHM) often experience slow postnatal growth and no clinical data is available to guide the duration of DHM for preterm infants. The investigators hypothesize that transitioning from DHM to preterm infant formula after the first month of life is both safe and conveys improved weight and length gains and fat free mass accumulation.