Non-phosphorylated IGFBP-1 is mainly synthesized by decidual cells in amniotic fluid, which separates from the chorionic membrane during labor, and the decidual cell fragments leak into the cervical mucus. The volume fraction of IGFBP-1 in the amniotic fluid is 100-1,000 times higher than in the mother’s blood. It is mainly used for the auxiliary diagnosis of premature rupture of fetal membrane in pregnant women.