Levels of insulin-like growth factor-binding protein-1 increase rapidly in amniotic fluid from 11 to 16 weeks of pregnancy.

Concentrations of IGF-binding protein-1 (IGFBP-1) were measured by radioimmunoassay in 176 amniotic fluid samples from 9 to 20 and 36 to 42 weeks of pregnancy. Low levels of IGFBP-1 were present at 9 and 10 weeks (median values 35.0 and 45.0 micrograms/l respectively). After 10 weeks, the levels increased by four orders of magnitude to reach a peak at 16 weeks (median 145.2 mg/l). After 16 weeks levels fell. Near term, the levels (median 27.1 mg/l) were lower than in the second trimester. The rapid increase in IGFBP-1 shown by radioimmunoassay was confirmed by Western ligand blotting. The findings suggest that the regulatory role of IGFBP-1 in the growth or differentiation of the fetus or of its surrounding membranes may change as pregnancy advances.