Fetal Insulin-Like Growth Factor (IGF)-I, IGF-II, and Ghrelin in Association with Birth Weight and Postnatal Growth in Monozygotic Twins with Discordant Growth

Objective: To investigate the relative contribution of genetic (fetal) vs. environmental (maternal/placental) factors on growth, we studied monozygotic twins with intertwin birth weight difference. Patients and Methods: Twenty-seven twins (15 with discordant growth) who have been treated for severe twin-to-twin transfusion syndrome by laser coagulation were studied. Cord blood samples were analyzed for IGF-I, IGF-II, IGF-binding protein-2, and ghrelin. Intertwin difference (Δ) of birth weight was correlated to Δ of the parameters analyzed. The Δ weight after 1 yr was correlated with Δ birth weight and all hormones. Results: The Δ birth weight was positively correlated with Δ IGF-I (r = 0.66; P < 0.0002) and negatively correlated with Δ IGF-binding protein-2 levels (r = −0.68; P < 0.001) but with neither Δ IGF-II nor Δ ghrelin. There was a strong intertwin correlation for all hormones. By comparing the growth in the first year, we found an overall reduction of the relative weight difference between the twins of 57%. ANOVA was used to calculate factors for prediction of postnatal catch-up growth. Besides the birth weight difference (R2 = 0.84; P < 0.0001), only ghrelin was of prognostic value for postnatal catch-up growth (R2 = 0.94; P = 0.0035). Conclusion: These data confirm the importance of IGF-I in contrast to IGF-II for fetal weight. Additionally, ghrelin seems to be involved in fetal and probably postnatal growth.