THE RELATIONSHIP BETWEEN GESTATIONAL AGE, SIZE AND NUTRITIONAL INTAKE AND GROWTH FACTORS IN PREMATURE INFANTS. † 1457

Abstract

The role of growth factors in early postnatal growth is poorly understood. The purpose of this study was (i) to examine the change in serum levels of IGF1, IGF2 and IGFBP3 with increasing gestational age (GA) and (ii) to explore the relationship between physical size, nutritional intake and growth factors. Weekly serum IGF1, IGF2 and IGFBP3 were determined using commercial immunoradiometric assays (Diagnostic Systems Laboratories, Webster, TX, USA) for the first 5 to 8 postnatal weeks of life in 22 premature infants (6M:16F; mean birth weight 1050g, range 735-1590g, mean GA at birth 27 weeks, range 24-31 weeks). Nine babies had bronchopulmonary dysplasia diagnosed on clinical and radiological grounds but were not treated with oral steroids. Daily weights (g), weekly occipital-frontal circumference (OFC)(cm) and total body length (TBL)(cm) were recorded as well as daily nutritional intake. There was no difference in weight gain, change in OFC and TBL, protein and caloric intake between infants with BPD and those without lung disease. Serum levels of IGF1, IGF2 and IGFBP3 increased significantly (r=0.56, 0.37 and 0.48 respectively, p<0.001) with gestational age. The mean serum level of IGF1 increased from 0.5 nmol/l at 25 weeks GA to 3.6 nmol/l at 37 weeks GA. Over the same time period, mean serum levels of IGF2 increased from 30 nmol/l to 61.0 nmol, and those for IGFBP3 increased from 0.35 mg/l to 1.0 mg/l. Body weight (g) was significantly correlated (p<0.001) with serum IGF1 (r=0.60), IGF2 (r=0.28) and IGFBP3 (r=0.51) while there was no correlation with OFC or TBL. Daily caloric intake (kcal/kg/day) was significantly correlated(p<0.001) with IGF2 (r=0.40) and IGFBP3 (r=0.42) levels, while protein intake (g/kg/day) was correlated with IGF1 (r=0.35). Using stepwise multiple linear regression analysis, GA, weight and protein intake accounted for 47% of variation in serum IGF1 levels, weight and caloric intake predicted 22% of variation in IGF2 levels and 35% of variation in IGFBP3 levels. Mean serum levels of all growth factors were lower in patients with BPD but using multiple linear regression analysis, the presence of BPD did not contribute further to the variation predicted by GA, weight and caloric or protein intake. We concluded that GA and weight each have an important influence on serum IGF1, IGF2 and IGFBP3 levels, while different components of nutritional intake affect specific growth factors.