Serum insulin-like growth factor I (IGF-I), IGF-binding proteins-1 and -3, and postnatal growth of late preterm infants.

Late preterm infants may have impaired early growth. The role of circulating insulin-like growth factors (IGFs) in the regulation of postnatal growth of these infants is unclear. The aim of the study was to investigate prospectively the serum levels of IGFs during the first year of life in late preterm infants and their association with birth weight and early postnatal growth. The study was conducted on 112 infants, born appropriate for gestational age (GA) at GA 32-36 weeks. Serum levels of IGF-I and IGF-binding proteins (IGFBP) -1 and -3, and anthropometric measurements were recorded at the chronological age of 2 and 6 weeks, and 3, 6, 9, and 12 months. The mean levels of both IGF-I and IGFBP-3 were found to be lower at 2 and 6 weeks, 82±44, 100±31 ng/ml, and 1.7±0.8, 2.1±1 µg/ml, respectively, but then rose and remained stable between 3 and 12 months. The levels of IGFBP-1 were lower at the 3 first study points and increased gradually thereafter. Birth weight correlated positively with the level IGF-I at 2 and 6 weeks (R=0.35, 0.37; p<0.01), but negatively at 12 months (R= - 0.34; p<0.01), independent of other factors. At all study points up to 6 months, the level of IGF-I was higher in infants who showed more rapid growth in either body weight or crown heel length. In late preterm infants, the serum IGF-I level is closely related to early accelerated growth. Its diverse associations with birth weight may imply a regulatory effect on regression of growth towards the mean.

Vitamin D and parathormone levels of late-preterm formula fed infants during the first year of life.

BACKGROUND/OBJECTIVES: Preterm infants are at risk for low vitamin D but documentation on late-preterm infants is sparse. This prospective study monitored longitudinally vitamin D and parathormone (PTH) levels in late-preterm formula fed infants during the first year of life, taking into consideration in utero and postnatal growth, and season and diet. SUBJECTS/METHODS: The study population comprised 128 infants of gestational age (GA) 32-36 weeks, of which 102 were appropriate (AGA) and the remaining 26 were small for GA (SGA). Serum levels of vitamin D (25(OH)D), PTH calcium, phosphate (P) and alkaline phosphate were estimated at 2 and 6 weeks, and at 3, 6, 9 and 12 months of age. RESULTS: The 25(OH)D levels were relatively low at 2 and 6 weeks in both AGA and SGA infants (21±11, 20±7 ng/ml and 25±16, 23±8 ng/ml, respectively), but increased at 6 months (45±14, 47±10 ng/ml) and remained stable thereafter. SGA infants had lower 25(OH)D levels at 9 and 12 months (AGA 45±14, 47±18 ng/ml vs SGA 38±13, 37±13 ng/ml, P<0.05). Deficiency of 25(OH)D (<20 ng/ml) was found in 18.5% of measurements in 92 (72%) infants, and its insufficiency (20-32 ng/ml) was found in 29.2% of measurements in 99 (77.3%) infants. Most measurements with vitamin D <32 ng/ml were observed at the first three study points, where PTH showed an inverse association with 25(OH)D, reaching a plateau thereafter. CONCLUSIONS: Late-preterm, formula fed infants may have suboptimal vitamin D levels and elevated PTH, especially, during the first 3 months. Those born SGA may have lower vitamin D levels up to the end of the first year of life.