72 Chapter 4 Methods Study Population This paper describes the results of the “Nutrition in relation to the endocrine regulation of preterm growth” (NUTRIE) study, a longitudinal observational study on nutrition in relation to the endocrine regulation of growth and body composition in preterm infants. Eighty-seven participants were enrolled between September 2015 and July 2018. Infants born between 24 and 32 weeks of gestation were eligible for study participation if they were born without substantial congenital anomalies, and were admitted to the neonatal intensive care unit (NICU) of Amsterdam UMC, location VU University Medical Center in Amsterdam, The Netherlands. Informed consent was obtained in the first week of life. The study was approved by the medical ethics committee of the VU Amsterdam and was registered at the Dutch Trial Register (www.trialregister.nl; NTR5311). Nutrition Infants initially received total parenteral nutrition and minimal enteral feeding. During total parental feeding, clinicians aimed to achieve an energy intake of 85– 100 kcal kg−1 day−1, a protein intake of 3–4 g kg−1 day−1, and a fat intake of 3–3.5 g kg−1 day−1. One the first day of life, parenteral glucose administration was targeted at 5.5–7 mg.kg−1 min−1, going up to maximum 12 mg kg−1 min−1 after the first week of life, depending on blood glucose levels. Full enteral feeding (160 mL kg−1 day−1) was aimed to be achieved within 7 to 10 days after birth with a total protein intake of 3.5 to 4.5 g kg−1 day−1 and a total energy intake of 110 to 140 kcal kg−1 day−1. Infants were primarily fed human milk. If own mother’s milk was insufficient or unavailable, donor human milk was administered up to 32 weeks PMA, followed by preterm starters formula until discharge home. If parents declined the use of donor human milk, infants were fed preterm starters formula from birth, whenever own mother’s milk was unavailable. Clinicians aimed to achieve 15–20 g weight gain kg−1 day−1, with a weight SD score above −1 SD. Head circumference growth was targeted at 1 cmper week and length at 1.25 cm per week. Breast milk fortifier (Nutrilon Nenatal Breast Milk Fortifier, Nutricia, Wageningen, The Netherlands) was added to human milk once an enteral intake of 100 mL kg−1 day−1 was achieved. In case of poor growth, as assessed by the clinician in charge, intake was increased to a maximum of 180 mL/kg, permitted that the infant’s condition allowed for an increased fluid intake. If poor growth persisted, up to 1% protein fortifier (Nutrilon Nenatal Protein Fortifier, Nutricia, Wageningen, The Netherlands) was added to the fortified human milk. Lastly, up to 4% of a highenergy, long-chain triglyceride, fat emulsion (Calogen, Nutricia, Wageningen, The Netherlands) was added if growth remained restricted despite fortification. In
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