Physical examination and anthropometric measurements (weight, length, and head circumference) at birth and at 3, 6, 9, 12, 18, and 24 months of age (Neonatology Unit CHUS) Blood levels of fatty acids in the first week of life and at 3 months, 6 months, and 12 months. (Metabolic Unit. Hospital de Cruces, Bilbao) Visual- and auditory-evoked potentials at 6 and 12 months of age (Neurophysiology Unit CHUS)