Hyponatremia is a common complication among preterm infants, renal losses of sodium
contribute to the development of hyponatremia in preterm newborns. Sodium imbalances impact
in newborns outcome. There is controversy about the time of initiation and the requirements
of sodium in premature infants. Hypothesis: early (24 hours of life) sodium supplementation
(5mEq/kg/day) prevents the develop of hyponatremia in preterm infants.