176 Chapter 8 Besides, a higher fat mass percentage and a higher fat mass index have been associated with an increased occurrence of metabolic syndrome components (35, 36). Therefore, monitoring body composition in early life would be a valuable asset to help to implement timely measures to prevent adverse outcomes on the long term. As discussed in chapter 6 and 7, diverse methods are available to estimate or measure body composition in preterm infants. Nevertheless, there is no consensus on which reference method should preferentially be used to assess body composition in infants. Meanwhile, the few comparative studies conducted till date show poor agreement. (37) . As reported in chapter 6 the measurement of skinfolds and anthropometry such as waist circumference, is easy to conduct without expensive equipment, but unfortunately estimates of fat mass based on thesemethods show poor agreement with air displacement plethysmography and dual-energy x-ray absorptiometry. Nevertheless our study had a small sample size and did not compare the different methods before term corrected age. Therefore at this point it remains to be concluded whether there should remain a place for skinfold measurements and alternative anthropometry during hospitalisation before term age. Furthermore, as described in our systematic review in chapter 7, overall validation studies have been conducted in small study cohorts and there is no method that qualifies as the gold standard in living infants. In conclusion, at this time, there is inconclusive evidence to advise one particular method for the assessment for body composition in preterm infants. In clinically stable subjects we would suggest using air displacement plethysmography which is minimally invasive, has a moderate workload and yields accurate results. Nevertheless, currently there is no air displacement devices available for infants weighing between 8 and 10 kg, which complicates long-term follow up. Alternatively, isotope dilution is an accurate method which could be used in infants who aren’t clinically stable and is not restricted to certain weight limits. However, it has a high workload. Currently it seems there are no easy-to-use, low-cost, bedside techniques available that yield accurate results. All-in-all further research is warranted, which should investigate instruments at different time points and consensus should be reach on which method should be used as a reference. Future research directions This thesis touched on the influence of nutrition, growth and the developing endocrine axis onoutcomes of preterminfants in early infancy. Additional outcomes of the NUTRIE study, such as neurodevelopment and risk factors for the metabolic syndrome, e.g. blood pressure and lipid profile, are yet to be reported. This will shed more light on the complex interplay between IGF-I and the development of preterm infants. Nevertheless, it can be concluded that adequate levels of IGF-I are required to ensure sufficient growth, a favourable body composition and to prevent major comorbidities. Using intra-uterine IGF-I levels as a reference, interventions are needed to increase IGF-I levels after preterm birth. This should preferably be done through non-invasive methods. Nevertheless, to date non-invasive methods,
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