93 IGF-I, growth and body composition in preterm infants 5 Introduction Preterm birth abruptly interferes with a prime stage of development. Not surprisingly, almost half of infants born preterm, show postnatal growth restriction by the time they are discharged from the hospital. (1, 2) In addition, preterm infants, compared to infants born at term, have been reported to have a higher fat mass percentage at term equivalent age. (3) Postnatal growth restriction, as well as increased fat mass in infancy, have been linked to impaired neurodevelopmental outcome. (4, 5) In addition, there are concerns that higher fat mass in early life is associated with adverse cardiometabolic outcomes in young adulthood. (6, 7) Therefore, it would be of interest to gain more insight in factors determining growth and body composition in early life, as a means to ameliorate later health outcomes in infants born preterm. Insulin-like growth factor I (IGF-I) plays a key role in the regulation of growth and body composition in early life. (8) Interestingly, the relationship between IGF-I and body composition has been reported to vary, depending on the timing of IGF-I and body compositionmeasurement. Based on previous studies, it could be speculated that high IGF-I levels between preterm birth and term equivalent age increase fat free mass, while from term age onwards higher IGF-I could be associated with more fat mass. (9-11) Nevertheless, only a few studies report on IGF-I in relation to body composition in preterm infants. Therefore, definitive conclusions on the relationship between IGF-I and body composition are yet to be drawn. This study aimed to explore the relationship between IGF-I, growth and body composition in preterm infants up to term equivalent age. To account for the possible impact of timing, IGF-I levels were assessed in different time frames between birth and term equivalent age and associations between changes in IGF-I, growth and body composition were explored. Methods Study population Ninety infants were enrolled between August 2015 and August 2018. (Figure 1) The study participants were part of the NUTRIE study (Nutrition in relation to the endocrine regulation of preterm growth study). This longitudinal observational study collected data on nutritional intake, linear growth, body composition and IGF-I levels between preterm birth and 2 years corrected age. Infants admitted to the neonatal intensive care unit (NICU) of the VU University Medical Center were assessed for eligibility if they were born at a gestational age of 24 weeks + 0/7 days up to and including 31 weeks + 6/7 days. Infants who had substantial congenital abnormalities were excluded. Informed consent was obtained within the first week of life.
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