Serum somatomedin C concentrations in the fetal sheep increase markedly during gestation

Serum somatomedin C concentrations in fetal sheep and pregnant ewes from days 51 to 149 of gestation were determined by specific radioimmunoassay. In the fetus (n = 61 samples) serum somatomedin C concentrations, fitted to a regression curve, increased significantly with advancing gestation from 0.44 units/ml at 51 days to 3.99 units/ml at 149 days, an increase of 806% (P less than 0.001). In the pregnant ewes (n = 14 samples), serum somatomedin C did not change during gestation. The temporal relationship between the marked increase in fetal somatomedin C concentrations and the acceleration of fetal growth is consistent with the hypothesis that somatomedin is important in the stimulation of fetal growth.