Phosphorylation profile of amniotic fluid hIGFBP-1. Amniotic fluid from F+/M– matings was assayed for total and nonphosphorylated hIGFBP-1, and the phosphorylation status of the protein was expressed as the ratio of the two values (nonphosphorylated/total hIGFBP-1). Data represent the mean of 15–25 samples of amniotic fluid. *P < 0.01 for e14.5 versus e17.5.