95 IGF-I, growth and body composition in preterm infants 5 and once at term equivalent age. A chemiluminescence immunoassay (LIAISON®, DiaSorin, Italy) was used for the analysis (intra-assay percent coefficient of variation (%CV): 8%, inter-assay %CV: 7%). Potential critical windows Based on previous studies investigating the influence of IGF-I on body composition, the following time frames were assessed to analyze the predictive value of (changes in) IGF-I and weight, length and head circumference SDS on body composition at term equivalent age: • 4 weeks postnatal age (PNA) and the change from birth to 4 weeks PNA (10); • 36 weeks PMA and change from birth to 36 weeks PMA (9); • The change from 30 weeks PMA to term equivalent age (14); • Term equivalent age (11). Potential confounders Nutrition Actual daily macronutrient intake was calculated from the intake documented in hospital records between birth and 36 weeks PMA and total macronutrient intake was assessed as a potential confounder. Infants were started off with minimal enteral feeding and total parenteral nutrition shortly after birth. Full enteral feeding (160 ml.kg-1.day-1) was aimed to be achieved within 7 to 10 days after birth. In case of poor growth, as assessed by the clinician in charge, enteral nutrition was supplemented with protein fortifier (Nutrilon Nenatal Protein Fortifier, Nutricia, Wageningen, The Netherlands) or fat emulsion (Calogen, Nutricia, Wageningen, The Netherlands). Infants were primarily fed their own mother’s milk. The average intake of own mother’s milk was 90% of the total enteral intake, supplemented with donor human milk or preterm starters formula, if parents declined donor human milk use. Donor human milk was only administered up to 32 weeks PMA, thereafter preterm starters formula was given if own mother’s milk did not suffice. During hospitalization no infants were exclusively formula fed. Comorbidities Data was collected on the occurrence of bronchopulmonary dysplasia (BPD), necrotizingenterocolitis (NEC), late-onset sepsis (LOS), intraventricular hemorrhage (IVH), persistent ductus arteriosus (PDA) and retinopathy of prematurity (ROP). The occurrence and severity of these conditionswere assessedas potential confounders. Other confounders Lastly, gender and ethnicity were assessed as a potential confounders.
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