Fetal serum levels of insulin, growth hormone and insulin-like growth factor-I in concordant and discordant twin gestations

Objective: To examine the role of insulin, growth hormone and insulin-like growth factor (IGF)-I in concordant and discordant twin pairs. Methods: Umbilical cord serum samples were obtained from 20 twin pairs with weight discordancy (intertwin birth weight difference > 20%) and from 20 concordant twins (intertwin birth weight difference < 20%), both groups of similar gestational age, gravidity, and parity. The serum samples were analyzed for the levels of IGF-I, growth hormone and insulin in both maternal and fetal compartments. Results: Among the group of discordant twins, the normally grown twin, in all cases, had significantly higher cord serum IGF-I levels than their growth-restricted co-twin (108 - 73 ng/ml vs. 39 - 24 ng/ml; p < 0.01). There were no significant intertwin differences in the cord blood IGF-I levels in the concordant twin pairs (87 - 44 vs. 88 - 48 ng/ml; p = 0.986). Insulin and growth hormone levels did not correlate with intertwin birth weight differences. Conclusion: These data demonstrate that IGF-I is important in the regulation of both normal and restricted fetal growth in utero, and its action appears to be, at least in part, through an endocrine action. The precise role of growth hormone and insulin in fetal growth restriction remains uncertain.