Serum somatomedin C, bioassayable growth-promoting activity (thymidine activity), and transferrin in human fetuses: in utero study.

Serum somatomedin C, thymidine uptake stimulating activity, and transferrin were measured in fetal blood collected by ultrasound-guided puncture of umbilical vessels in utero during prenatal assessment for mother-to-fetus transmissible infections. Serum somatomedin C and transferrin were measured by immunoassay. Thymidine activity was measured by assay of [3H]thymidine incorporation into lectin-activated human lymphocytes. Studies were conducted in 48 healthy fetuses at gestational ages 21-28 wk. From 21-24 to 25-28 wk, serum somatomedin C significantly increased from 0.05 +/- 0.06 to 0.24 +/- 0.03 U/ml, while thymidine activity significantly decreased from 1.41 +/- 0.15 to 0.95 +/- 0.06 U/ml. Transferrin levels did not change. These data suggest that the humoral control of fetal growth at midpregnancy involves mechanisms other than direct regulation by somatomedin.