Somatomedin activity in human cord plasma and relationship to birth size, insulin, growth hormone, and prolactin.

Somatomedin activity was determined by a rabbit chondrocyte bioassay in cord plasma from babies of between 37 and 41 wk gestation. A positive correlation (P less than 0.001) was found between plasma somatomedin activity and birthweight. The mean somatomedin activity in infants whose birthweights were within 1 SD of the mean (3293 g) was 0.76 +/- 0.27 U/ml. Mean somatomedin activity in infants whose weight was (a) greater than the mean weight +1 SD was 1.3 +/- 0.17 U/ml, and (b) less than the mean weight -1 SD was 0.48 +/- 0.15 U/ml. Plasma somatomedin activity was also correlated with placental weight, P less than 0.02 and gestational age, P less than 0.05. No correlation was found between plasma somatomedin activity and birth length, OFC, most measurements of skinfold thickness, cord plasma, growth hormone, prolactin or insulin.