The purpose of this study is to evaluate the growth, and the general, visual, and language development of preterm infants fed different formulas and/or human milk. The formulas vary in the type of fat they contain. Two important fatty acids present in human milk, but not aavailable commercially available, are docosahexaenoic acid (DHA) and arachidonic acid (AA). This study will evaluate the effect of adding sources of DHA and AA to formulas. This controlled randomized parallel study will be conducted at 7 sites around the world.