Insulin-like growth factors in amniotic fluid.

The concentrations of insulin-like growth factors I and II (IGF-I and IGF-II) in amniotic fluid were determined by specific immunoassays in 58 women. IGF-I concentrations were constant throughout gestation at approximately 20 ng/ml; the mean IGF-II concentration was 114 +/- 13 (+/- SE) ng/ml at the earliest period of gestation studied and remained unchanged at 26 to 33 weeks despite a greater than 50% decrease in amniotic fluid total protein. A precipitous decrease in IGF-II concentration occurred at term which was not explainable by alterations in total amniotic fluid protein concentration. The concentrations of IGF-I and IGF-II in amniotic fluid did not correlate with concentrations of these factors in maternal serum (r = 0.08 and 0.09, respectively). [125I]IGF-I and [125I]IGF-II, after incubation with amniotic fluid, bound to a 40-45 K protein (or proteins). A carrier protein of greater mol wt, as in serum, was not detected. These findings indicate that there is dynamic control of IGF in amniotic fluid during normal pregnancy.