Objectives: To study whether intrauterine growth restriction (IUGR) is associated with decreased sensitivity to the main fetal growth factor, insulin, and the effect of glucocorticoid therapy on insulin sensitivity in preterm infants.
Study design: Newborn infants with a birth weight (BW) of< 1500 g were classified as appropriate for gestational age ([AGA], BW within +/- 1 SD, n = 10), or small for gestational age ([SGA], BW <-2 SD, n = 13); 5 AGA infants and 8 SGA infants received systemic steroids. An abbreviated modified minimal model test was performed, consisting of sequential blood samples for glucose and insulin assays, and intravenous infusions of 0.3 g/kg glucose and 0.02 U/kg regular human insulin. The insulin sensitivity index (S(I)) was calculated using a computer program.
Results: The basal insulin/glucose ratio (I/G) and S(I) did not differ between the AGA and SGA groups. Steroids did not influence the I/G nor the S(I) of AGA infants (10.2 +/- 6.7 vs 8.2 +/- 2.3), but decreased the S(I) in the SGA group (12.2 +/- 5.1 vs 5.3 +/- 2.7, P <.05).
Conclusions: Insulin sensitivity of neonates can be measured by the modified minimal model. IUGR is not associated with impaired fetal glucose tolerance. Early neonatal steroid treatment decreases insulin sensitivity in SGA infants, which may contribute to their risk of having hyperglycemia.