Study 1 The content of protein in the milk of mothers, who delivers prematurely, is about a third higher than in the milk from the mother who delivers on time. The nutritional composition changes over time and the content of protein decrease. Therefore the premature infant is at risk of protein deficiency. While the infant is feeding by tube this decreasing content of protein can made up by adding, while it is more difficult when the infant is exclusively breastfeeding. The hypothesis is that reduced protein content in breast milk is associated to a fewer number of days where the premature infant is exclusively breastfed.