Insulin-like growth factor-binding protein 1 (IBP-1) also known as placental protein 12 (PP12) is a protein that in humans is encoded by the IGFBP1 gene. IGFBP-1 plays an important and potentially beneficial role in regulating metabolic and vascular homeostasis. The structures reveal the mechanisms of insulin-like growth factor (IGF) signaling regulation via insulin-like growth factor-binding proteins (IGFBP) binding. PROM (premature rupture of fetal membranes) is a major risk to the mother as well as to the fetus because it is also associated with an increased risk of intra-amniotic infection that may lead to neonatal sepsis. Rupture of fetal membarnes is not always associated with significant leakage of amniotic fluid and hence PROM is not always easy to diagnose and some of the historical methods do not provide adequate sensitivity or specificity. PROM may be diagnosed using IGFBP-1 as a marker. IGFBP-1 concentration in amniotic fluid rises during preganancy and 100 to 1000 fold higher concentrations may be detected in amniotic fluid compared to human blood. Because of the high concentration even minute amounts of amniotic fluid may be detected in samples taken from vagina when PROM is suspected.