Study design: prospective, longitudinal, multicenter trial in 3 Neonatal Intensive Care Units in Ile de France. Specific aim is to compare the developmental changes of melatonin in preterm and term newborns (200 infants and their mothers: 4 groups of 50 infants: 24-27GA +6d ; 28-32 GA +6d ; 33-36 GA +6d ; 37-41 GA +6d). Secondary aims are the following: