The present invention relates to amniotic fluid specific polypeptide and a method for detecting rupture of the amniotic membranes. In particular the invention provides a marker for prolonged rupture of the membranes (PROM), which marker consists essentially of polypeptides of approximately 75 kDa, 20 kDa and 50 kDa as determined by 4-15% gradient SDS-PAGE under reducing conditions.