Initiation of human parturition. V. Progesterone binding substance in fetal membranes

This study was undertaken as part of an investigation of the potential role of progesterone metabolism within fetal membranes in the initiation of human labor. The results of this study provide evidence that a progesterone binding substance is present in amnion and chorion laeve during the last few days of pregnancy. This substance binds progesterone, cortisol, and 5alpha-dihydroprogesterone but does not bind 20alpha-hydroxy-4-pregnen-3-one, R 5020, or dexamethasone. We conclude that this is a previously undescribed progesterone binding substance and propose a possible mechanism by which this substance may be involved in the initiation of human parturition.