Amino Acid and Acylcarnitine Profiles in Premature Neonates

Primary Hypotheses of the study include: * Metabolic profiles are influenced by gestational age, chronological age, type and degree of nutritional support and illness * Metabolic profiles differ between neonates who receive commercial formula and neonates who receive primarily human breast milk * Neonates who develop parenteral associated cholestasis have metabolic markers that identify at risk patients (high serum urea nitrogen, citrulline, histidine, methionine, and succinyl carnitine and low thyroxine, serine and glutamate) * Neonates that have hypothyroidism have abnormal metabolic profiles (low tyrosine levels)