184 Chapter 9 Pretermbirthdisrupts a key phase of humandevelopment. Immature organ systems have to guide the growth and development of the preterm infant which results in an increased risk of several comorbidities, including postnatal growth failure. This thesis focused on the postnatal modulation of growth and body composition in very preterm and extremely preterm infants. Furthermore, the influence of nutritional intake and the immature endocrine axis on health outcomes was investigated. The background of this thesis is discussed further in Chapter 1. Part I. IGF-I and nutrition in relation to growth, body composition and health outcomes in preterm infants In chapter 2 a review of the literature demonstrated that preterm infants are at risk of impaired growth and a suboptimal body composition. It was shown that IGF-I levels in the period between preterm birth and term age play a pivotal role in the regulation of growth from preterm birth through to infancy and seem to influence body composition up to childhood. Low IGF-I levels between preterm birth and term age were associated with impaired growth up to term age and possibly an unfavourable body composition at term equivalent age. IGF-I levels were also associated with nutritional intake: higher caloric and protein intake were associated with higher IGF-I levels from a gestational age from 30 weeks onwards. Indeed in chapter 4, nutritional intake was associated with IGF-I levels. In particular between 30 and 33 weeks postmenstrual age, higher macronutrient and total caloric intake were associated with higher IGF-I levels. Furthermore, parenteral nutrition in the second week of life, which is the major source of nutrition at that time, was found to be associated with lower IGF-I levels. The review of literature in Chapter 2 also demonstrated that both higher IGF-I levels as well as increased protein intake improved neurodevelopmental outcome in preterm infants. In addition, Chapter 3 showed that low IGF-I levels between preterm birth and 36 weeks postmenstrual age increased the odds of BPD. Furthermore, a higher intake of donor human milk increased the odds of BPD. Hence there may be a window of opportunity to increase IGF-I levels through nutritional interventions and thus improve growth, body composition and health outcomes in infants born preterm. Part II. Determinants and assessment of body composition in preterm infants There are concerns that infants born preterm have a less favourable body composition in infancy, i.e. lower fat free mass, compared to infants born at term. This in turn may be associated with adverse cardiometabolic outcomes in later life. Despite these concerns, there are no guidelines on which methods should
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