As in healthy term babies, the ideal food for preterm infants and sick term babies is breast milk. There are many studies indicating that the composition of breast milk can vary from mother to mother, according to the gestational week of the baby and gender. In new researches on breast milk content; It is argued that breast milk is different during the day and at night, that the micro and macro nutrient content, hormones and some enzymes show different levels of secretion at different times of the day, and that breast milk has a circadian rhythm.

This research is designed as a prospective, randomized, controlled type. The study will be carried out in order to evaluate the effect of Chronobiological Approach Nutrition Model application on baby's growth parameters and discharge time in preterm babies hospitalized in Neonatal Intensive Care Unit (NICU).

Simple randomization method will be used for the study and the babies will be divided into intervention(n=40) and control groups(n=40). The research was carried out with 80 babies followed up in the neonatal intensive care unit.

The milk of the intervention group patients will be matched circadian and given to the babies, the milk of the control group patients will be given without matching according to the clinical routine practice. Demographic data, anthropometric measurements (weight, height, head circumference of all babies will be recorded in the "Baby Monitoring Form" created by the researcher.

Circadian fluctuations in breast milk content are very important in preterm infants fed with expressed breast milk. The composition of breast milk varies throughout the day. In the literature, there is no randomized controlled study suggesting that the breast milk of infants fed with expressed milk should be matched to the baby circadian. In this study, it was aimed to evaluate the effect of Chronobiological Approach Model application on preterm infants growth parameters and discharge time in feeding of preterm infants hospitalized in the neonatal intensive care unit . It is aimed to accelerate the growth of babies by making circadian matching to breast milk in feeding preterm infants and to increase the quality of nursing practices by reducing the length of hospital stay.

Inclusion Criteria:

• Birth weight >1400 <2500 gram and gestational week ≥32-37 weeks
• Who are feeding only human milk
• Fully enterally fed babies (50-100ml / kg / day)
• Whose parents signed the informed consent to participate in the study were included.

Exclusion Criteria:

• Infants who cannot feed with human milk
• Who receive intravenous fluid, total parenteral nutrition or mixed fluid
• Infants with major congenital, cardiac, respiratory or airway abnormalities and infants who require additional pressure and respiratory support
• Metabolic imbalances, hypoglycemia or electrolyte imbalance
• Narcotic analgesic or sedation therapy
• Whose parents did not sign the informed consent were excluded.