77 IGF-I and nutrition in preterm infants 4 Figure 2. Insulin-like growth factor 1 (IGF-1) levels in extremely preterm and very preterm infants. Compared to boys, at birth, IGF-1 levels were lower in girls. In addition, IGF-1 levels had an inverse relationship with gestational age at birth and PMA at the time of sampling. Postnatal age in days at the time of sampling did not predict IGF-1 levels. After correcting for weight, IGF-1 levels were no longer predicted by gender, gestational age at birth, and postmenstrual age at the time of blood sampling either, and weight remained the only significant predictor of IGF-1 levels. IGF-1 Levels in Relation to Growth Mean birth weight SDS was 0.04, with three out of 87 infants being small for gestational age (weight SDS <−1.3) (Figure 3). At 36 weeks PMA 17 out of 80 infants had a weight SDS below −1.3 SDS. Between the second week of life and 36 weeks PMA, five out of 80 infants showed catch-up growth (increase in weight SDS > 0.67). IGF-1 positively correlated with previous, concurrent, and subsequent weight and weight SDS. When weight SDS was corrected for absolute weight in grams, only weight remained a significant predictor of IGF-1 levels. Compared to infants with a weight of 1000 g or more, infants with a weight below 1000 g had a 2.5 nmol/L lower IGF-1 at two weeks postnatal age (95% CI −3.7–−1.3, p< 0.001).
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