Longitudinal changes in insulin-like growth factor-I, insulin sensitivity, and secretion from birth to age three years in small-for-gestational-age children
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Introduction: Insulin resistance ( IR) develops as early as age 1 to 3 yr in small for gestational age ( SGA) infants who show rapid catch- up postnatal weight gain. In contrast, greater insulin secretion is related to infancy height gains. We hypothesized that IGF-I levels could be differentially related to gains in length and weight and also differentially related to IR and insulin secretion. Methods: In a prospective study of 50 SGA ( birth weight < 5th percentile) and 14 normal birth weight [ appropriate for gestational age ( AGA)] newborns, we measured serum IGF-I levels at birth, 1 yr, and 3 yr. IR ( by homeostasis model assessment) and insulin secretion ( by short iv glucose tolerance test) were also measured at 1 yr and 3 yr. Results: SGA infants had similar mean length and weight at 3 yr compared with AGA infants. SGA infants had lower IGF- I levels at birth ( P < 0.0001), but conversely they had higher IGF- I levels at 3 yr ( P < 0.003) than AGA infants. Within the SGA group, at 1 yr IGF- I was associated with length gain from birth and insulin secretion ( P < 0.0001); in contrast at 3 yr IGF- I was positively related to weight, body mass index, and IR. Conclusions: IGF- I levels increased rapidly from birth in SGA, but not AGA children. During the key first- year growth period, IGF- I levels were related to beta- cell function and longitudinal growth. In contrast, by 3 yr, when catch- up growth was completed, IGF- I levels were related to body mass index and IR, and these higher IGF- I levels in SGA infants might indicate the presence of relative IGF-I resistance.