Analyzes of criteria of judgment The principal analysis will compare the rate of children deprived of melatonin between the 4 groups. This comparison will be carried out by a test of the chi-2 or Fisher if suitable. Nevertheless this analysis will be refined by modeling the plasmatic secretion according to the gestational age and of the hour of melatonin measurement. This modeling will use either a mixed model, or a nonlinear model like the models used into pharmacokinetic. In the same way will be modeled the urinary levels of melatonin and in the mother's milk by taking of account the same parameters as previously and the repetition of the measurements. Some parameters will be used like variables of adjustment like the luminous environment, the preeclampsia, the sex, the intrauterine growth restricted infants, multiple pregnancies, the way of childbirth.