Longitudinal Changes in Insulin-Like Growth Factor-I, Insulin Sensitivity, and Secretion from Birth to Age Three Years in Small-for-Gestational-Age Children

Abstract

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. 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. 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. 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.