 The study took place in a single-center; it is a prospective randomized study of preterm infants less than 1500 grams andor less than 32 weeks gestational age, admitted to the Neonatal Intensive Care Unit in the University Clinical Hospital of Santiago de Compostela. They were recruited for a period of 14 months from July 2010 to august 2011 and followed from birth until 2 years of life. 