Figure 1.

Labor (term and preterm) is characterized by increased myometrial contractility, cervical dilatation, and rupture of the chorioamniotic membranes. Collectively, these events have been referred to as the “common pathway of parturition.” The switch of the myometrium from a quiescent to a contractile state is associated with a change in nuclear progesterone receptor isoforms and an increase in the expression of the miR-200 family, as well as an increase in estrogen receptor α signaling. Cervical ripening is mediated by changes in extracellular matrix proteins, as well as changes in epithelial barrier and immune surveillance properties. Decidual/membrane activation, in close proximity to the cervix, occurs in preparation for membrane rupture, and to facilitate separation of the chorioamniotic membranes and placenta from the uterus. E: epithelium; M: mucus; Os: cervical os.