31 Dietary proteins and IGF I levels in preterm infants 2 However after term age contradictory findings have been reported. Several studies observed IGF I levels to positively correlate with current growth parameters and preceding growth velocity in pretermas well as healthy term infants (18, 19, 25, 26). In contrast findings concerning the correlation between IGF I levels and subsequent growth velocity are inconclusive (Table 1). Table 1. Associations between IGF I and growth Van de Lagemaat (18) Van de Lagemaat (18) Giapros (19) Chellakooty (25) Ong (24) Socha (26) Study population Very preterm infants Very preterm infants Late preterm infants Healthy term infants Healthy term infants Healthy term infants Timing IGF I blood draw Term age 3 months 6 weeks, 3 & 6 monthsb 3 months 3 months 6 months IGF I & previous growth velocity ↗Δ weight SDS (birth - term age) ↗Δ length SDS (birth - term age) ↗Δ weight SDS (birth - 3 monthsa) ↗Δ length SDS (birth - 3 monthsa) ↗ weightc ↗ lengthc ↗Δ weight SDS (birth - 3 months) ↗Δ length SDS (birth - 3 months) Not reported ↗ΔWFL SDS (birth - 6 months) IGF I & current growth ↗ weight and length SDS ↗ weight and length SDS ↗ weight and length SDS ↗ weight; → length ↗ weight; →length ↗ WFL SDS IGF I & subsequent growth velocity ↘Δ weight SDS (term age - 6 monthsa) ↘Δ length SDS (term age - 6 monthsa ) →Δ weight SDS (3 - 6 monthsa ) →Δ length SDS (3 - 6 monthsa) → (growth parameters not specified) ↘Δ weight SDS (3 - 18 months) →Δ length SDS (3 - 18 months) →Δ weight (3 - 12 months) ↗Δ length (3 - 12 months) →Δ WFL SDS (6 – 12 months) ↗ = positive correlation; ↘ = negative correlation; → = no correlation; Δ = gain; a = correctedage; b = chronological age; c = higher IGF I levels in infants with accelerated previous weight and length gain (a difference of more than 0.67 SDS between two study points); IGF I = Insulin-like growth factor I; SDS = standard deviation score; WFL = weight-for-length Hypothesizing these findings might reflect that after term age a turning point occurs. At this point infants with the lowest IGF I levels and thus the poorest previous growth may tend to show accelerated growth. This hypothesis would be in line with the negative correlation between IGF I and subsequent growth velocity found in the above stated studies: infants with the lowest IGF I levels had the highest subsequent growth velocity. Less comorbidity in preterm infants after term age might create a less stressful environment in which catch-up growth could occur, i.e. an increased growth rate compared to the infant’s previous growth
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