Bibian van der Voorn

125 EARLY LIFE GROWTH ON CORTISOL AFTER PREMATURITY We used the following definitions 19 : 1. Appropriate for gestational age (AGA) 1 : birth weight and birth length > –2SDS 2. Growth restriction (AGA GR+): weight and/or length ≤–2SDS at 6 mo. corrected age, after being born AGA 3. Small for gestational age (SGA): birth weight and/or birth length ≤–2SDS 4. Catch-up growth (SGA CUG+): weight and length >–2SDS at 6 mo. corrected age, after being born SGA For STEP-2, children aged 8 y visited the outpatient clinic in the morning. Venous blood sampleswereobtainedafter anovernight fast, andanthropometricmeasurementswere performed. Weight was measured to the nearest 0.05 kg with an electronic scale (Seca) and standing height was measured to the nearest 0.1 cm using a digital stadiometer (DGI 250D, De Grood Metaaltechniek, Nijmegen, the Netherlands), and expressed as SDS based on Dutch reference data adjusted for gender and age 18 . Salivary samples for cortisol measurement were collected at 4 moments: prior to bedtime at the evening before the study visit, immediately after awakening at the morning of the study visit, 15min after awakening, and before lunch during the study visit. Participants were instructed to refrain from eating and drinking at least 30min before sampling. Parents were asked to report their education level, which was categorized as neither, one, or both parent(s) having finished higher education. The study protocols were approved by the ethics committee of VUMC, Amsterdam. All parents of subjects gave written informed consent. LABORATORY PARAMETERS Serum was stored at −80°C and thawed only once just before the analyses. In STEP-1, total serum cortisol (nmol/L) was measured using 2 different methods as the assay changed during the course of the study. In 90 infants, total serum cortisol at term age, 3 mo. and 6 mo. corrected age was measured using a competitive immunoassay (Advantage, Nichols Institute Diagnostics, San Juan Capistrano, USA) with an intra-assay coefficient of variation (CV) of 3%, 3% and 4% (at levels of 100, 500 and >600 nmol/L, respectively), an inter-assay CV of 8%, 7% and 6% (at levels of 140, 400 and 850 nmol/L, respectively), and a lower limit of quantitation (LLOQ) of 30 nmol/L. In 62 infants, total serum cortisol at term age, 3 mo. and 6 mo. corrected age was measured using a competitive immunoassay (DPC, Los Angeles, USA) with an inter-assay CV of 8%, 7% and 6% (at levels of 150, 400 and 900 nmol/L, respectively).