94 Chapter 5 The NUTRIE study was powered to detect a medium size effect (r = 0.35) of IGF-I on fat mass percentage. To that end, a sample size of at least 62 infants was required (power 80%, significance 5%). With an expected dropout rate of 10%, the aim was to include 70 infants. The study was approved by the medical research ethics committee of the VU University Medical Center and was registered in the Dutch trial register (www. trialregister.nl; NTR5311). Study procedures All participants were admitted to the NICU of the VU University medical center within 24 hours of birth. Infants were discharged to step-down clinics in other hospitals when the clinical condition permitted to do so and the infants had reached a postmenstrual age (PMA) of at least 30 weeks and a weight of at least 1000 grams. Clinical data was collected up to 36 weeks PMA or discharge home, whichever came first. Infants were invited for follow-up at term equivalent age. Growth From birth to hospital discharge, weight, length and head circumference were measured weekly by the nursing staff. Weight was measured to the nearest gram on an electronic scale. Length was measured with a length board to the nearest 0.5 cm. Occipital-frontal head circumference was measured to the nearest 0.1 cmwith a non-stretchable measuring tape. At the follow-up visit growth was measured in the same way by two investigators. Fenton growth charts were used to calculate weight SDS. (12) Growth restriction was defined as a weight SDS under the tenth percentile (-1.3 SD). (1) Body composition Fat mass and fat-free mass were measured at term equivalent age through air displacement plethysmography (ADP), using the PeaPod®. Infants weremeasured nude and hair was smoothened using hair oil. Movement was allowed, but in case of excessive crying the measurement was stopped. All measurements were done by two investigators. In line with the manufacturer's guideline, quality control checks were done daily and the PeaPod® scale was calibrated every two weeks. A more detailed description of the PeaPod®measurements can be found elsewhere. (13) The coefficient of variation for repeated measurements has been reported to lie between 0.02% and 0.09%.(13) IGF-I IGF-I was sampled from umbilical cord blood at birth, followed by venous or capillary blood sampling from the infant every other week up to 36 weeks PMA
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