• daily rhythm;
  • fetal distress;
  • melatonin;
  • newborn;
  • pineal gland;
  • premature

Abstract: In order to assess the existence of a rhythmic secretion of melatonin (aMT) in newborns and whether this rhythm is affected by neonatal stress, we studied 112 newborns classified in three groups: normal babies delivered at term, preterm infants born before the 38th week, and babies with fetal distress. Melatonin was measured by RIA in the umbilical artery and vein at the time of birth. Melatonin levels in umbilical arterial and venous blood showed a diurnal rhythm in all groups. Melatonin levels in umbilical cord artery and vein were closely related. Nocturnal melatonin levels were increased in newborns with acute fetal distress in comparison with normal term and preterm neonates. These results suggest that (1) a rhythm of aMT secretion exists in newborns, although it cannot be determined whether this rhythm is of maternal or fetal origin and (2) neonatal stress (acute fetal distress) increases aMT production during the night in comparison with normal term and preterm neonates.