The most ideal method for providing breast milk is breastfeeding. However, it may be necessary to express breast milk for reasons such as the newborn being in an intensive care unit, the mother being hospitalized for any reason, or the mother starting to work. The content of breast milk varies according to gestational age and stages of lactation. However, it varies from day to day depending on the infant's needs. In recent literature, it is emphasized that the content of breast milk (carbohydrates, fats, proteins, vitamins, trace elements, etc.) varies according to circadian variation. In the literature review, no national or international study was found indicating whether the circadian properties of breast milk have an effect on the infant's growth parameters. This study was designed as a randomized controlled experimental study to determine the effect of the circadian properties of breast milk on the growth parameters of the infant and the absorption levels of nutrients by the baby in preterm newborns.

no effect on the infant's growth parameters and nutrient absorption levels by the infant.

Hypothesis 1 (H1): Feeding preterm newborns with breast milk according to the circadian rhythm has an effect on the weight of the infants.

Hypothesis 2 (H2): Feeding preterm newborns with breast milk according to the circadian rhythm has an effect on the height of the infants.

Hypothesis 3 (H3): Feeding preterm newborns with breast milk according to the circadian rhythm has an effect on the head circumference of the infants.

Hypothesis 4 (H4): Feeding preterm newborns with breast milk according to the circadian rhythm has an effect on the absorption levels of vitamins and trace elements measured in the infants' breast milk.

Breast milk is an ideal and unique food with excellent content for the healthy growth and development of both term and preterm babies. Breast milk, which is considered the "Gold Standard" in term and preterm baby nutrition, has a complex, lively and dynamic structure. The content of breast milk varies from day to day and according to the gestational age, stages of lactation, and the baby's needs. These differences indicate that breast milk is a unique food.

Breast milk contains many complex nutrients, and while the amount of some nutrients varies depending on the mother's diet, lactation day and duration, some nutrients remain at relatively constant levels. Breast milk contains macronutrients (carbohydrates, proteins, fats), micronutrients (vitamins, trace elements and electrolytes) and bioactive factors (various hormones, immune factors and other bioactive factors). In recent years, the difference in the content of breast milk according to circadian variation has been evaluated. In studies examining breast milk content according to circadian variation, it was stated that total carbohydrate concentration did not show circadian change.It has been determined that the fat concentrations in breast milk, which are necessary for the growth and development of the baby, indicate the existence of circadian variation. However, there are different results in element and vitamin studies. In cases where breast milk should be given by expressing, not giving milk in accordance with the circadian rhythm may disrupt the developing circadian rhythms of babies, potentially causing sleep problems and decreased physiological harmony with their parents/environment. This situation may negatively affect the baby's growth and development and endanger its health. In light of this information; The study was planned to determine the effect of the circadian properties of breast milk on the growth parameters of the baby and the absorption levels of nutrients by the baby in preterm newborns.

Inclusion Criteria:

• The mother is healthy (without a history of preeclampsia, hypertension, diabetes, hepatitis B or C, HIV, tuberculosis, mastitis or oncological disease)

• The mother's birth is 32-34 between weeks of gestation

• The mother does not follow a special diet

• The mother is not a vegetarian

• The mother does not smoke

• The mother must have a body mass index within normal limits (BMI = 18.50-24.99) (WHO, 2022b)

• Income must be at or above the monthly minimum wage

• The mother cannot breastfeed her baby and routinely expresses her own milk every three hours.

• The mother expresses her milk with a milking machine (milking will be done with the same brand device and the same level of suction power).

• The baby is in the neonatal intensive care unit

• Feeding the infant by gavage and oral method

  *In order for the preterm newborn to be fed effectively and safely orally, it is necessary for the preterm baby to be able to coordinate sucking-swallowing as well as breathing (Tian et al., 2015). Gavage feeding is a priority in babies who have this coordination (TND, 2018). In babies who have the coordination of sucking, swallowing and breathing, oral feeding will be started after an assessment of readiness for oral feeding will be made.

• Full enterally fed babies

• The infant does not have a health problem that requires surgical treatment

• 10th-90th percentile curves according to the infant's gestational age. percentile (those with normal birth weight for gestational age: Appropriate for Gestational Age -AGA)

Exclusion Criteria:

• The mother receives medication (antibiotics, etc.) treatment
• Interruption of the mother's milk during the working period
• Low birth weight of the baby according to the intrauterine growth curve
• Feeding the baby with formula
• Total parenterally fed babies
• The baby has a small birth weight for the gestational age (Small for Gestational Age - SGA) and a baby with a large birth weight for the gestational age (LGA).

Criteria for Exclusion from the Study;

• The mother received medication (antibiotics, etc.) during the data collection process.
• The mother does not want to continue
• Respiratory problems, hypoglycemia, hyperbilirubinemia, etc. in preterm babies. occurrence of various problems

Single (participant) blinding was used in the study. For this purpose, it was not stated which group the participating mothers were in the research, but they were informed about the procedure to be performed. Therefore, a separate informed consent form was prepared for each group. Statistician blinding will also be applied. While coding the research data, the research group will be coded as A and B, and the statistician will be prevented from knowing which letter represents which group.