The Effect of a Chronobiological Feeding Model on Growth Parameters and Length of Hospitalization in Preterm Infants: A Randomized Controlled Study

Abstract

Background and Purpose:

Preterm infants are born before the 37th gestational week and need prompt nutrition. The circadian rhythm is an internal 24-hour cycle regulated by endogenous molecules. Human milk contains different biological peptides at different times within this cycle. Chrononutrition is a feeding model that is adjusted to match the biological clock of the individual. This study tests chrononutrition as a superior feeding model in preterm infants. This study aimed to evaluate the effect of the chronobiological feeding model on growth parameters and discharge time among preterm infants.

Methods:

We conducted a prospective, randomized controlled trial in a tertiary neonatal intensive care unit between October 2021 and March 2022, randomized preterm infants to receive either chrononutrition (study group = 45) or standard feeding (control group = 46), and used the infant’s follow-up form for data collection.

Results:

Among 91 neonates, the median gestational age was 33 weeks, and the mean birth weight was 2,100 g. Demographic findings and growth parameters showed no difference between the groups (p > 0.05). Weight gain and percentile measurements at discharge were statistically significantly higher in the study group (p = 0.002 and p = 0.003, respectively). Discharge time was statistically significantly lower after full enteral feeding and hospitalization time was shorter in the study group (p = 0.001).

Conclusions:

The chronobiological feeding model showcased significant positive effects on anthropometrics and percentile measurements at discharge and led to a 2-day reduction in the length of hospital stay.

Introduction

Human milk is the ideal food for infants since it contains all the nutrients, hormones, and immunological and biological factors that support growth and development.^1,2 As in healthy full-term infants, breastfeeding should be the first choice in preterm infants.³ Preterm infants are infants born before the 37th gestational week with deficient macronutrient stores and they require urgent nutrition. Their organs and systems do not mature fully, especially the gastrointestinal system. Hence, they suffer from difficulties in coping with metabolic imbalances.³ It is crucial for preterm infants to be breastfed during their stay in the neonatal intensive care unit (NICU) and they need support in oral feeding with practices that facilitate the transition to breastfeeding.⁴

Research has shown that limiting nutrition to certain times of day can positively affect health, which has paved the way for the field of chrononutrition. Chrononutrition is the practice of eating the optimal type and amount of food based on one’s biological clock.⁵ (Flanagan) Preterm infants have different daily activities, feeding, and resting practices from adults and these factors change as infants develop. Human milk consumption throughout the day and the night is of great significance, given the biological differences between the two time frames. Also, the concentrations of the components in human milk vary based on the mother’s circadian rhythm.^6,7

The composition of human milk can vary based on many factors, including biochemical differences during lactation, mother’s diet content, breastfeeding time, foremilk/hindmilk, infant’s sex, infant’s age, gestational week, and the time of day.^8,9 Unlike infant formula, the content of human milk changes throughout the day to meet the shifting physiological needs of the infant.^10,11 Day milk contains higher cortisol levels, which improves wakefulness, feeding behaviors, and catabolic processes, as well as amino acids that regulate activity levels.¹² Night milk, on the contrary, contains high levels of melatonin and tryptophan, which promote sleep, relieve digestion, and support cell regeneration.¹²

Humans have an internal circadian rhythm that supports environmental changes like light, temperature, noise, food, and exercise.¹³ Circadian rhythm is a biochemical cycle mechanism that allows organisms to synchronize their physiology and behavior with the geophysical time; it is stimulated by external factors, particularly daylight and metabolic cadence.¹⁴ The circadian fluctuations in the composition of human milk help transfer this shifting biochemistry from the mother to the infant based on the time of day.¹⁵ The disruption of the circadian rhythm during pregnancy can cause adverse outcomes, like an increased likelihood of miscarriage or preterm birth and low birth weight.¹⁶ A disturbed circadian rhythm during pregnancy can also have negative consequences on growth in the first year of life.¹⁷

The preterm infants lose hormonal cues, normally received in utero, and are prematurely exposed to circadian synchronizers like daylight and enteral feeding. To date, little attention has been paid to rhythmic cues in NICUs. Generally, the circadian synchronizers known from NICU guidelines are illumination and sound levels.¹⁸ Other synchronizers in NICUs include feeding practices, caregiving, incubator temperature, phototherapy, sleep disruptions, and the timing of care procedures and medications. Currently, there are no clinical recommendations for the timing of exposure to these synchronizers. The Circadiem trial studies for very preterm infants in the NICU have generally focused on light and noise exposure.¹⁹ However, what is not being addressed in that trial is supporting rhythmicity by administration of circadian time-matched human milk since variations in the composition of nutritional intake may be more physiological.²⁰

The effects of chrononutrition, an important circadian cue for preterm infants, have not been clinically investigated so far. In a NICU setting, neonatal enteral feeding is provided regularly, with consistent quantity and timing. McKenna and Reiss have suggested a chronolactomics approach to feeding and breast milk composition for preterm infants in the NICU. Recent evidence suggests that human milk can act as a Zeitgeber, as its composition varies throughout the day.¹ According to White, the diurnal and nocturnal variations in human milk could influence infant growth and development, while Gilst suggests that providing circadian-matched milk may improve circadian development, as well as support the neonate’s growth and health.¹⁸

When breastfeeding is not an option in hospitalized preterm infants, expressed human milk is used.⁴ In NICUs, expressed human milk is often refrigerated and then thawed and warmed upon need. Healthcare workers often use the available expressed human milk at hand regardless of the time of expression. This human milk may be exposed to certain industrial practices during storage or may suffer from circadian changes because it is not given to the infant at the time of expression.¹²

Breast milk, with its changing content according to day and night, allows infants to distinguish between day and night, and this is called “chrononutrition.”²¹ Most knowledge of chrononutrition comes from adult studies and does not fully apply to developing humans. Newborns feed day and night, unlike adults, and this is biologically significant. Milk composition changes with the mother’s circadian rhythms, and infants are sensitive to both milk and environmental circadian cues.⁶

This research investigated the effects of the chronobiological feeding model on preterm infants based on the fact that human milk has a circadian rhythm. This study aimed to evaluate the effect of the chronobiological feeding model on growth parameters and discharge time among preterm infants.

Materials and Methods

Design and setting

This was a randomized controlled trial that was conducted between October 2021 and March 2022 at a NICU of Zeynep Kamil Maternity and Child Diseases Training and Research Hospital in Turkey.

The research data were collected from the NICU of a training and research hospital providing tertiary neonatal intensive care services. Our NICU is a multidisciplinary NICU with 63 beds and 95 nurses. Our NICU received the “Baby-Friendly Hospital” title in 1998 and the “Baby-Friendly NICU” title in 2014.

Ethical approval

This study was approved by the institutional review board and strictly followed the institution’s ethical guidelines (date: December 23, 2020, number: 199). The legal guardians of all the participants signed written informed consent forms prior to enrollment. The clinical trial number was NCT04992819.

Inclusion/exclusion criteria

Our sample included infants who were born at 32^0/6–36^6/7 gestational weeks and hospitalized in the NICU, fed only with human milk, and whose mothers received training on expressing and storing human milk. The exclusion criteria included intrauterine growth restriction, major congenital anomalies, antenatal steroid use (since antenatal steroids can increase maturation and therefore impact randomization), postnatal surfactant use, and total parenteral nutrition. We also excluded infants with feeding intolerance, sepsis, necrotizing enterocolitis, congenital metabolic disease, symptoms of vomiting and diarrhea, hypoglycemia, or electrolyte imbalance, and infants whose feeding was interrupted for more than 24 hours. Finally, infants who received mechanical ventilation support, narcotic analgesia, or sedation, and participants who did not receive breastfeeding training were excluded. Flow chart for selection of eligible infants were given in Figure 1.

FIG. 1.

Flow chart for selection of eligible infants in the study.

Randomization

We used the URN (urn randomization) method for randomization. Purple balls represented the study group and yellow balls represented the control group. The researcher placed all the balls in a black bag and asked the nurses on shift to draw a ball out of the bag. The data collector (first author) could not be assigned as a blind evaluator. Each infant was assigned to one of the two groups based on the color of the ball drawn, thus ensuring their random distribution. As a result, the sample consisted of 91 infants (45 in the study group and 46 in the control group).

The sample was composed of infants who met the inclusion criteria and whose mothers agreed to participate in the study. We conducted a power analysis (G*Power 3.1.9.2) to determine the sample size based on similar previous research.^22,23 The effect size was 0.05, the test power was 0.97, and the minimal sample size was 45 infants in each group.

Study intervention

In our NICU, infant feeding and breastfeeding practices are conducted in accordance with the recommendations of the Baby-Friendly Initiative and the National Neonatology Society Guidelines, which are regularly updated to align with the latest international standards.²⁴ All expressed human milk is stored in a dedicated refrigerator within a designated human milk preparation room. These milk samples are prepared and used based on their arrival date, without implementing circadian-matching practices.

We filled out a preterm infant descriptive information form and a preterm infant follow-up form for each infant in the sample. Yellow (day) and purple (night) stickers were attached to milk storage bags to separate day and night milk. We used 25 milk storage bags for each mother. We did not use any labels for the control group.

Filling out the infant follow-up form, application of the intervention

The observing nurse filled out a data collection form for the infants of both groups. All infants were followed up with the standard feeding practice of the NICU before, during, and after feeding. The infants in the study group received circadian-matched human milk. Only the prefeeding application was different in the study group and the other procedures were carried out similarly in both groups during and after feeding.

Prefeeding interventions

Study group (preterm infants fed by the chronobiological feeding model)

Within the scope of this research, we informed the mothers and nurses who prepared the human milk about the research. These mothers were asked to transfer the milk expressed between 08:00 and 19:59 (daytime) into yellow milk bags and the milk expressed between 20:00 and 07:59 (night) into purple milk bags. For circadian-matching of human milk, we chose 12-hour intervals (08:00–19:59, 20:00–07:59) to best correspond with the times of day when considerable changes in the circadian rhythm occur. Since there was no place for the mothers to stay at our NICU, we determined the time periods as 12-hour cycles and collected the data at the end of these cycles. The nurses at the enteral nutrition preparation room prepared these human milk samples based on expression time and matched them according to the circadian cycle.

Control group (preterm infants fed by the NICU’s routine)

These infants were fed in accordance with the standard practices of the NICU. The mothers were asked to transfer the expressed milk to the milk bags they were already using and to bring them to the NICU. Only the expression date was written on these milk bags. The nurses at the enteral nutrition preparation room prepared these human milk samples by date and stored them without any time-matching practice.

Feeding order interventions

The feeding was performed by the primary nurse of the infant. Oral feeding was carried out with a small teat on a slow-flow bottle in accordance with the NICU’s routine. The infant was placed in a semi-raised side position for oral feeding. The infant was bottle-fed in a flexible, semi-upright position, swathed at an angle of 45–60°. All infants in the study were fed with a cue-based feeding approach based on physiological and behavioral signs. To ensure physiological stability during oral feeding, SpO₂ > 90%, HR: 120–160/min and respiration: 40–60/min measurements were considered normal. Feeding was performed in line with the infant’s hunger and stress symptoms. Pushing the pacifier away, avoiding the bottle, turning its tongue away, spreading fingers, showing tension and extension in extremities, yawning, hiccuping, and gagging were considered signs of stress. For infants who displayed non-normal physiological or behavioral signs, feeding was interrupted for 30 minutes to rest.²⁵

Postfeeding interventions (study and control groups)

Each feeding practice was completed within 30 minutes to avoid the infant’s fatigue. The short resting intervals during feeding were evaluated within the feeding period. Feeding was considered successful when the infant consumed 80% of the provided human milk. Additionally, the duration of feeding was indicated as the time from the moment the bottle was provided to the infant to the end of the feeding. After feeding, the infant was placed in the lying position on the right side while maintaining the flexion posture.²⁵

All infants were bottle-fed until the mother started breastfeeding. The LATCH scale is used in the clinical routine to evaluate the transition to breastfeeding. The nutritional status was evaluated based on the discharge criteria of the NICU. Infants with successful breastfeeding results in the last 24 hours (LATCH score > 7) were discharged and switched to full breastfeeding. The research continued until all infants were discharged.

Data collection

The time it takes for preterm infants to transition to full enteral feeding varies based on some infant characteristics. The preterm infants in this research were enrolled on the mean 11th postnatal day (min–max: 1–28). Each infant was monitored until discharge; this period took a mean of 7–9 days (min–max: 3–17). According to the Turkish Neonatology Society (TND), the discharge criteria for preterm infants include demonstrating adequate weight gain, breathing independently without the need for respiratory support, and successfully transitioning to full oral feeding, whether via bottle-feeding or breastfeeding. Furthermore, the infant should demonstrate metabolic and physical stability, as well as the ability to maintain body temperature independently, without requiring incubator support. Data collection was conducted in three stages:

Stage 1: The study was initiated with infants who met the inclusion criteria and whose mothers agreed to participate in the study. In the study, randomization was conducted according to the recommendations of the TND, when infants’ daily food intake reached 50–100 mL/kg/day, marking the transition to full enteral feeding. The intervention was initiated when the infant transitioned to full oral feeding, a critical phase in which the infant gains independent feeding ability and metabolic functions stabilize. The criteria for full oral feeding included meeting all nutritional needs through oral feeding (bottle feeding), stopping total parenteral nutrition, coordination of sucking, swallowing, and breathing, absence of feeding intolerance symptoms, and regular weight gain. Due to the COVID period, preterm infants were fed by nurses in the NICU until discharge. We initiated the follow-up period, and the observing nurse recorded the demographic data of the infants and anthropometric measurements of their deliveries on the preterm infant follow-up form.

Stage 2: We measured body weight just before 08:00 a.m. daily feeding from the initiation of full oral feeding (day 0) to discharge and recorded this data on the infant follow-up form.

Stage 3: We performed a weekly follow-up of the infant’s anthropometric measurements. Weight, height, and head circumference were measured on the 1st, 7th, and 14th days based on the length of stay and plotted on a Fenton growth chart. Data were recorded on the infant follow-up form at the 1st day (birth), 7th day (1st week), and 14th day (2nd week).

We used Drager and Tende brand incubators to measure the body weights of the preterm infants. The infants were naked during all measurements; we made all measurements at 08:00 a.m. before feeding, with the infants in the supine position and the incubators in a flat position. Head circumference was measured using a nonflexible tape measure belonging to the researcher. Height was measured using a length board. We used a Mamajoo brand feeding bottle specifically designed for preterm infants. The teats had a slow and natural flow rate that was suitable for preterm infants, were made of silicone, did not contain latex, and were suitable for reuse after sterilization. We used a Lansinoh brand human milk storage bag provided by the researcher. We labeled the circadian-matched human milk samples using tags that were prepared by the researcher and used these labels for the training of the mothers in the study group. We used a large Vestel brand refrigerator in the NICU for the storage of the circadian-matched human milk samples. We placed the human milk samples of the control group on a different shelf in the same refrigerator. In line with hospital procedures, the temperature of the refrigerator was monitored and recorded twice a day. Finally, we used a Sumer brand thermostatic heater to warm the human milk samples to 36°C before feeding.

Measurements

The primary outcomes were monitoring the growth parameters of the infants, including body weight, height, and head circumference. All infants were evaluated from the beginning of the study until the day of discharge. Body weight values were recorded daily. Height and head circumference measurements were recorded weekly. The secondary outcomes were weight gain, height, and head circumference measurements and their percentile values at discharge from the hospital, as well as length of hospital stay.

Data analysis

We used the Number Cruncher Statistical System (NCSS) 2007 software for all statistical analyses (Kaysville, Utah, USA). Descriptive data were given as mean, standard deviation, median, frequency, percentage, and minimum and maximum values. We used the Shapiro–Wilk test and performed graphical investigations to test the conformity of the quantitative data to normal distribution. We conducted an independent samples t-test for comparisons of normally distributed quantitative variables and the Mann–Whitney U test for comparisons of non-normally distributed quantitative variables. We carried out a repeated measures analysis for in-group comparisons of normally distributed quantitative variables and the Bonferroni correction for pairwise comparisons. We used the Friedman test for in-group comparisons of non-normally distributed quantitative variables and the Wilcoxon signed-ranks test with Bonferroni correction for pairwise comparisons. Finally, we performed Pearson’s chi-squared test to compare qualitative data. The level of statistical significance was set at p < 0.05.

Results

Table 1 shows a comparison of the descriptive characteristics of the study and control groups.

Table 1.

Comparision of Descriptive Characteristics of the Preterm Infants (n = 91)

Characteristic	Descriptives	Study (n = 45)	Control (n = 46)	p
Gestational week	M ± SD	33.38 ± 1.37	33.46 ± 1.41	NS
Postmenstrual week	M ± SD	34.76 ± 2.00	34.20 ± 1.77	NS
Gender (%)	Female	27 (60.0)	25 (54.3)	NS
Gender (%)	Male	18 (40.0)	21 (45.7)	NS
APGAR (1 min)	M ± SD	7.33 ± 0.83	7.33 ± 1.06	NS
APGAR (5 min)	M ± SD	8.53 ± 0.59	8.70 ± 0.55	NS
Birth weight (g)	M ± SD	1998.44 ± 324.21	2116.3 ± 293.77	NS
Birth length (cm)	M ± SD	44.33 ± 2.58	45.26 ± 2.61	NS
Head circumference at birth (cm)	M ± SD	31.27 ± 1.8	31.62 ± 1.74	NS
Total parenteral nutrition (day)	M ± SD	6.69 ± 4.03	6.48 ± 3.97	NS
Full enteral feeding starting (100 mL/kg/day)	M ± SD	11.24 ± 6.67	11.63 ± 5.81	NS

APGAR, appearance pulse grimace activity and respiration; NS, nonsignificant; SD, standard deviation; M, mean.

There was no statistically significant difference in body weight, height, or head circumference between the infants (p > 0.05). However, the differences in weight (p = 0.002), height (p = 0.001), and the increases in weight and height percentiles from birth to discharge were significant only in the study group (p = 0.004, p < 0.01, p = 0.01; p < 0.05, respectively). Moreover, the rate of increase in weight percentile from birth to discharge was significantly higher in the study group (p = 0.003). Table 2 shows a comparison of the anthropometric measurements of the study and control groups.

Table 2.

Comparison of Anthropometric Measurements of the Preterm Infants (n = 91)

Anthropometry	Descriptives	Study (n = 45)	Control (n = 46)	Test/p
Birth weight (g)	M ± SD	1998.44 ± 324.21	2116.30 ± 293.77	NS
Before intervention weight (g)	M ± SD	2048.67 ± 312.87	2030.65 ± 269.70	NS
Discharge weight (g)	M ± SD	2278.56 ± 322.50	2247.17 ± 233.39	NS
Discharge weight (g)	Test/p	F: 61,845; 0.001**b	F: 47,062; 0.001**b
From birth to discharge weight difference (g)	Difference	280.11 ± 234.62	130.87 ± 185.34	Z: −3.085,0.002**a
From birth to discharge weight difference (g)	p	0.001**	0.001**	Z: −3.085,0.002**a
Birth height (cm)	M ± SD	44.33 ± 2,58	45.26 ± 2,61	NS
Before intervention height (cm)	M ± SD	44.89 ± 2.50	45.36 ± 2.47	NS
Discharge height (cm)	M ± SD	45.43 ± 2.52	45.95 ± 2.49	NS
Discharge height (cm)	Test/p	χ²: 79,656; 0.001**c	χ²: 79,358; 0.001**c
From birth to discharge height (cm)	Difference	1.09 ± 0.62	0.69 ± 0.40	Z: −3.550,0.001**a
From birth to discharge height (cm)	p	0.001**	0.001**	Z: −3.550,0.001**a
Birth head circumference (cm)	M ± SD	31.27 ± 1.80	31.62 ± 1.74	NS
Before intervention head circumference (cm)	M ± SD	31.50 ± 1.57	32.00 ± 1.56	NS
Discharge head circumference (cm)	M ± SD	32.00 ± 1.66	32.52 ± 1.45	NS
Discharge head circumference (cm)	Test/p	F: 19.256; 0.001**b	F: 20.403; 0.001**b
From birth to discharge head (cm)	Difference	0.73 ± 0,99	0.90 ± 1.20	NS
From birth to discharge head (cm)	p	0.001**	0.001**	NS
Before intervention weight (10–90 percentile)	M ± SD	13.16 ± 14.95	12.57 ± 11.92	NS
Discharge weight (10–90 percentile)	M ± SD	17.64 ± 17.69	11.70 ± 10.50	NS
Before intervention discharge weight (10–90 percentile)	Difference	4.49 ± 11.47	−0.87 ± 6.26	Z: −2.970, 0.003
Before intervention discharge weight (10–90 percentile)	p	Z: −2.889; 0.004**d	NS	0.003**a
Before intervention height (10–90 percentile)	M ± SD	64.58 ± 28.02	70.80 ± 30.70	Z: −1.072
Discharge height (10–90 percentile)	M ± SD	68.76 ± 27.26	71.26 ± 31.04	Z: −0.552
Before intervention discharge height (10–90 percentile)	Difference	4.18 ± 11.49	0.46 ± 1.75	NS
Before intervention discharge height (10–90 percentile)	p	Z: −2.585; 0.010*	NS	NS

*p < 0.05, **p < 0.01.

Mann–Whitney U test.

Repeated measures test.

Friedman test.

Wilcoxon signed-ranks test.

M, mean; NS, nonsignificant; SD, standard deviation.

Table 3 displays a comparison of the length of hospital stay, hospitalization time, and postmenstrual age values at discharge between the study and control groups after switching to full oral feeding. Length of hospital stay and postmenstrual age at discharge did not differ statistically significantly between the groups (p > 0.05). After the transition to full oral feeding, hospital stay was shorter in the study group (p = 0.001).

Table 3.

Comparison Between the Groups Hospital Stay Day and After Full Enteral Feeding Hospital Stay Day (n = 91)

Hospital stay (day)	Descriptives	Study (n = 45)	Control (n = 46)	Test/p
After full oral feeding hospital stay (day)	M ± SD	7.04 ± 2.33	9.26 ± 3.57	Z: −3.263, ^a0.001^**
Hospital stay (day)	M ± SD	18.33 ± 8.25	16.76 ± 7.86	NS
Discharge postmenstrual week	M ± SD	35.93 ± 1.34	35.74 ± 1.97	NS

p < 0.01.

Mann–Whitney U test.

M, mean; NS, nonsignificant; SD, standard deviation.

Discussion

Preterm births and NICU admissions constitute the most common reasons for the discontinuation of breastfeeding.²² Human milk provides great benefits not only for healthy term infants but also for preterm infants.²⁶ Human milk protects preterm infants from serious complications like necrotizing enterocolitis, sepsis, bronchopulmonary dysplasia, and retinopathy of prematurity, reducing the length of hospital stay and rehospitalization rates.^27,28 Feeding preterm infants with human milk promotes brain development, improving their growth.²⁹ When an infant is born very preterm, it loses the temporal signals received from the mother prematurely and becomes totally dependent on 24/7 care in the NICU, where day/night rhythmicity is usually blurred.¹⁸ Disruption of 24-hour rhythms in the NICU may extend hospital stays, lower weight gain, and cause long-term health effects. McKenna and Reiss have suggested a chronolactomics approach to feeding and breast milk composition for preterm infants in the NICU. Human milk, with its composition changing throughout the day, may serve as a Zeitgeber.¹² Preterm infants chrononutrition, a crucial circadian cue, but has not yet been clinically investigated.³⁰ There is a gap in the literature regarding randomized controlled research on chrononutrition and its impact on nutrition and growth in infants. Although there are numerous recommendations for chrononutrition in adults, research suggests that circadian regulation in food intake helps protect metabolic health.^31,32

Preterm birth weight, height, and head circumference measurements were similar between the two groups in our study, with no statistically significant difference. The mean anthropometric measurements of preterm infants in both groups were similar before the implementation of the chronobiological feeding model (Table 1). There was no statistically significant difference between the groups in terms of birth weight and discharge weight measurements. However, the change in discharge weight versus birth weight was significantly higher in the study group (Table 2). Based on these findings, the chronobiological feeding model does not directly affect weight gain in preterm infants, but it may improve weight gain over time. Previous research has observed no circadian change in the total protein and carbohydrate content of human milk.^4,33 On the contrary, almost all relevant studies around the world have found circadian differences in fat content, which meets nearly half of the body’s need for energy.^33,34 The increase in body weight at discharge in our study group could be associated with circadian-matched feeding and appropriate fat content in circadian-matched human milk. In the fetus, the circadian rhythm can first be observed at the 30th week of pregnancy, although it is not fully functional in the early postnatal period.³⁵ Our study was conducted with preterm infants at the 32^0/6–36^6/7 gestational week, where the development of the circadian rhythm occurs. In this context, we determined that the development of the circadian rhythm continued in preterm infants fed with circadian-matched human milk. This practice did not lead to a significant difference in terms of body weight, but the change in discharge weight versus birth weight was significantly higher in the study group. The presence of artificial light and disharmony between the time of day and the hormonal cues passed through human milk can negatively affect circadian growth in infants.³⁶ Despite its benefits, the NICU environment includes challenges like noncyclical lighting, controlled temperatures, noncircadian feeding, and limited mother–infant contact. Circadian-matched human milk feeding is recommended for high-risk infants, as disturbed circadian rhythms can impair growth and development.³⁰ Here, we found no statistically significant difference between the groups of infants in terms of height or head circumference measurements at birth or at the time of discharge. Similarly, previous studies on various feeding models did not observe an effect on height in infants. However, our study group showed significantly greater height at discharge compared to birth, suggesting that chrononutrition positively affects growth (Table 2).

The main goal in feeding preterm infants is to catch the intrauterine growth rate. The attainment of growth means that the infant reaches the appropriate weight level for its age. In other words, the weight, height, and head circumference should reach the 50th percentile for that age.³ In our study, the percentile values at birth and discharge did not differ significantly between the groups. However, the mean increase in the weight and height percentile measurements at discharge was significant in the study group. This is the most striking finding in the present research for demonstrating the significance of appropriate intervention on the circadian cycle based on standardized anthropometry over an average of 20 days. Adequate growth is critical in preterm infants, especially in those with a low birth weight. Research reports that nearly 50% of these infants display weights below the 10th percentile on the growth charts at discharge; about 30% are even classified below the 3rd percentile.³⁷ In our study, a similar growth rate was observed, with almost all of the infants being discharged between the 3rd and 10th percentiles. A previous review suggests that circadian-matched human milk feeding positively affects growth, development, circadian rhythm development, and overall health.^15,30

NICUs should consider oral nutrition as a medical treatment and manage it in the same way. According to our findings, postmenstrual age and total hospitalization time at discharge were similar between the groups. However, after achieving full oral feeding, the infants in the study group had a significantly shorter hospital stay (Table 3). Interventions by neonatal nurses are of critical importance in promoting adequate sleep.³⁸ By feeding infants with circadian-matched human milk, they can regulate their sleep patterns and positively affect their growth and discharge times. Additionally, the hospitalization period following the starting of full oral feeding was found to be two days shorter in the study group. This suggests that using the chronobiological feeding model when providing expressed human milk to preterm infants could be highly beneficial.

Under Baby-Friendly NICU practices, breastfeeding is a key responsibility for neonatal nurses. Mothers should start expressing milk within the first 6 hours after birth and be trained in this process. Infants usually coordinate sucking, swallowing, and breathing around 36 weeks, but younger infants are fed expressed milk. Mothers need training on milk expression and storage. Neonatal nurses should be trained in chrononutrition, and all expressed milk should be labeled with date and time. These simple organizational changes, along with circadian-matched human milk storage practices, can promote the development of circadian rhythm in infants.³⁹

Limitations

This is a preliminary study on relatively large preterm infants, and more comprehensive studies should be conducted. Moreover, since there is no other randomized controlled research on the chronobiological feeding model, we discussed the findings in comparison with other studies that are related to the circadian rhythm.

The research process coincided with the COVID-19 pandemic period when NICU visits were prohibited in our country’s hospitals, and mothers were restricted from seeing their infants.

Conclusion and Implications for Practice

The amount of weight gain at discharge and the change in percentile measurements compared to birth were found to be higher in our study group. Although total hospitalization time and postmenstrual age were found to be similar across the groups, the time to discharge after full enteral feeding was shorter in the study group. In line with these results, we conclude that oral feeding preterm infants with circadian-matched human milk positively affects growth and shortens hospital stay.

Our data suggest that NICUs should consider using the chronobiological feeding model and provide training to mothers starting from the pregnancy period. Also, NICU staff can be motivated to develop innovative tools for circadian-based nutrition. Further research should investigate neurological, behavioral, and physiological effects in infants fed with the chronobiological feeding model. With contribution from further research, knowledge of chrononutrition, its usefulness, and the spread of these practices can motivate NICU workers to develop innovative tools for circadian-based nutrition.

Footnotes

Acknowledgments

The authors would like to thank the nursing staff and the doctors for their help, as well as the newborn infants and their parents for contributing to this article. This study is completed as a Doctorate Thesis at Istanbul Okan University, Institute of Graduate Studies, Pediatric Nursing Department.

Authors’ Contributions

E.T., G.U., and N.K. contributed to the conception and design of the study, literature review, writing of the article, data analysis, data collection, drafting critical revision, supervision, and editing. All authors are in agreement with the final version of the article and declare that the content has not been published elsewhere.

Ethical Approval

Ethical approval was provided by the institutional review board of Zeynep Kamil Women and Children’s Diseases Training and Research Hospital in advance of implementation. Written informed consent was obtained from the patients/guardians.

Disclosure Statement

The authors have no funding to disclose.

Funding Information

This research was supported by TUBITAK. Project No. 221S514.

References

Lyons

, Ryan

, Dempsey

, et al. Breast milk, a source of beneficial microbes and associated benefits for ınfant health. Nutrients, 2020; 12(4):1039; doi: 10.3390/nu12041039

Hermansson

, Kumar

, Collado

, et al. Breast milk microbiota ıs shaped by mode of delivery and ıntrapartum antibiotic exposure. Front Nutr, 2019; 6:4; doi: 10.3389/fnut.2019.00004

Kültürsay

, Bilgen

, Türkyılmaz

. Turkish Neonatal Society guideline on enteral feeding of the preterm infant. Turk. Arch. Pediatr, 2018; 53(Suppl 1):109–118.

Temizsoy

, Uysal

. Preterm bebeklerin beslenmesinde kronobiyolojik yaklaşim modeli: Sirkadiyen beslenme. Yoğun Bakım Hemşireliği Dergisi, 2022; 26(1):27–34.

Flanagan

, Bechtold

, Pot

, et al. Chrono-nutrition: From molecular and neuronal mechanisms to human epidemiology and timed feeding patterns. J Neurochem., 2021; 157(1):53–72; doi: 10.1111/jnc.15246

Caba-Flores

, Ramos-Ligonio

, Camacho-Morales

, et al. Breast milk and the importance of chrononutrition. Front Nutr, 2022; 9:867507; doi: 10.3389/fnut.2022.867507

Christian

, Smith

, Lee

, et al. The need to study human milk as a biological system. Am J Clin Nutr, 2021; 113(5):1063–1072.

Kim

, Yi

. Components of human breast milk: From macronutrient to microbiome and microRNA. Clin Exp Pediatr, 2020; 63(8):301–309; doi: 10.3345/cep.2020.00059

Perrella

, Gridneva

, Lai

, et al. Human milk composition promotes optimal infant growth, development and health. Semin Perinatol, 2021; 45(2):151380; doi: 10.1016/j.semperi.2020.151380

10.

Galante

, Milan

, Reynolds

, et al. Sex-specific human milk composition: The role of infant sex in determining early life nutrition. Nutrients., 2018; 10(9):1194.

11.

Hosseini

, Valizadeh

, Hosseini

, et al. The role of infant sex on human milk composition. Breastfeed Med, 2020; 15(5):341–346.

12.

Hahn-Holbrook

, Saxbe

, Bixby

, et al. Human milk as “chrononutrition”: Implications for child health and development. Pediatr Res, 2019; 85(7):936–942.

13.

Mc Kenna

, Karl

, Reiss

. The case for a chronobiological approach to neonatal care. Early Human Dev, 2018; doi: 10.1016/j.earlhumdev.2018.08.012

14.

Reddy

, Reddy

, Sharma

. Physiology, Circadian Rhythm. In: StatPearls. StatPearls Publishing: Treasure Island, FL; 2023.

15.

Italianer

, Naninck

EFG

, Roelants

, et al. Circadian variation in human milk composition: A systematic review. Nutrients, 2020; 12(8):2328; doi: 10.3390/nu12082328

16.

Caba

, González-Mariscal

, Meza

. Circadian rhythms and clock genes in reproduction: İnsights from behavior and the female rabbit’s brain. Front Endocrinol (Lausanne), 2018; 9:106; doi: 10.3389/fendo.2018.00106

17.

Kaur

, Teo

, Shukri

, et al. Circadian rhythm and its association with birth and infant outcomes: Research protocol of a prospective cohort study. BMC Pregnancy Childb, 2020; 20:96.

18.

Van Gilst

, Puchkina

, Roelants

, et al. Effects of the neonatal intensive care environment on circadian health and development of preterm infants. Front Physiol, 2023; 14:1243162; doi: 10.3389/fphys.2023.1243162

19.

CIRCA DIEM Trial Information. 2000. Impact. Available from: https://impact.psanz.com.au/clinical-trials/circa-diem-trial-information/

20.

Serón-Ferré

, Mendez

, Abarzua-Catalan

, et al. Circadian rhytm in the fetus. Mol Cell Endocrinol, 2012; 349(1):68–75.

21.

Aydan Aksoy

, Bekar

. Circadian breastfeeding: ımpact on maternal and ınfant health. Inst Health Sci J, 2023; 8:341–345; doi: 10.51754/cusbed.1311790

22.

Thakkar

, Rohit

, Ranjan Das

, et al. Effect of oral stimulation on feeding performance and weight gain in preterm neonates: A randomised controlled trial. Paediatr Int Child Health, 2018; 38(3):181–186.

23.

Fontana

, Menis

, Pesenti

, et al. Effects of early intervention on feeding behavior in preterm infants: A randomized controlled trial. Early Hum Dev, 2018; 121:15–20; doi: 10.1016/j.earlhumdev.2018.04.016

24.

Maastrup

, Haiek

, Neo-BFHI Survey Group. Compliance with the “Baby-friendly Hospital Initiative for Neonatal Wards” in 36 countries. Matern Child Nutr, 2019; 15(2):e12690; doi: 10.1111/mcn.12690

25.

Girgin

, Gözen

, Karatekin

. Effects of two different feeding positions on physiological characteristics and feeding performance of preterm infants: A randomized controlled trial. J Spec Pedıatr Nurs, 2021; 23:12214.

26.

Edmond

, Bahl

, WHO. Optimal feeding of low-birth-weight infants. Technical Review. ISBN 9241595094. Available from: http://www.who.int/maternal_child_adolescent/documents/9241595094/en/ [Last accessed: December 20, 2023].

27.

Miller

, Tonkin

, Damarell

, et al. A systematic review and meta-analysis of human milk feeding and morbidity in very low birth weight ınfants. Nutrients, 2018; 10(6): 707.

28.

Boquien

. Human milk: An ıdeal food for nutrition of preterm newborn. Front Pediatr, 2018; 6:295.

29.

Blesa

, Sullivan

, Anblagan

, et al. Early breast milk exposure modifies brain connectivity in preterm infants. Neuroimage, 2019; 184:431–439.

30.

White

. Circadian variation of breast milk components and implications for care. Breastfeed Med, 2017; 12(7):398–400.

31.

Franzago

, Alessandrelli

, Notarangelo

, et al. Chrono-nutrition: Circadian rhythm and personalized nutrition. Int J Mol Sci, 2023; 24(3):2571; doi: 10.3390/ijms24032571

32.

Challet

. The circadian regulation of food intake. Nat Rev Endocrinol, 2019; 15(7):393–405; doi: 10.1038/s41574-019-0210-x

33.

Hollanders

, Kouwenhoven

SMP

, van der Voorn

, et al. The association between breastmilk glucocorticoid concentrations and macronutrient contents throughout the day. Nutrients, 2019; 11(2):259; doi: 10.3390/nu11020259

34.

Paulaviciene

, Liubsys

, Molyte

, et al. Circadian changes in the composition of human milk macronutrients depending on pregnancy duration: A cross-sectional study. Int Breastfeed J, 2020; 15(1):49; doi: 10.1186/s13006-020-00291-y

35.

Wong

, Wright

, Spencer

, et al. Development of the circadian system in early life: Maternal and environmental factors. J Physiol Anthropol, 2022; 41(1):22; doi: 10.1186/s40101-022-00294-0

36.

Selalmaz

, Uysal

, Zubarioglu

, et al. The effect of intermittent and continuous feeding on growth and discharge time in very low birth weight preterm infants. Sisli Etfal Hastan Tip Bul, 2021; 55(1):115–121; doi: 10.14744/SEMB.2020.31549

37.

Thoene

, Anderson-Berry

. A review of best evidenced-based enteral and parenteral nutrition support practices for preterm infants born <1500 grams. Pediatr Med, 2018; 1:6–6.

38.

Park

. Sleep promotion for preterm ınfants in the NICU. Nurs Womens Health, 2020; 24(1):24–35; doi: 10.1016/j.nwh.2019.11.004

39.

Temizsoy

. Preterm, düşük doğum ağırlıklı ya da hasta bebeklerde emzirme ve Anne Sütü İle beslenme. In: Emzirme ve Anne Sütü ile Beslemede Danışmanlık/Güncel Yaklaşımlar. 1. Baskı. ( Özsoy

., ed.) Türkiye Klinikleri: Ankara; 2021, pp. 99–109.