Background: Human milk is the optimal source of nutrition for preterm infants. However, breast milk alone is often not sufficient to satisfy the high nutritional needs for growth and development in preterm infants. Fortified human breast milk is the best way to meet the nutritional needs of preterm infants. Human breast milk is fortified according to the estimated nutrient content of mature breast milk; however, because the content of breast milk is highly variable, the macronutrient support may be more or less than needed. The goal of this study was to analyze the macronutrient content of preterm human milk during the first 6 weeks of lactation.