Anatomy and physiology of the uterine cervix.

The human uterine cervix undergoes extensive changes during pregnancy. Collagen is reorganized and consolidated early in gestation with proliferation and hyperplasia of the cellular component. As term approaches, multiple factors work together in complex interactions that cause collagen dispersion and the cervix to ripen (clinically become softer). Increases in decorin levels, hyaluronic acid, and physiologic cell death are in part responsible for this remodeling process. As the collagen bundles disperse and lose strength, cytokines, hyaluronic acid, collagenases, and elastase possibly work together to allow effacement. Then, the mechanical forces of uterine contractions extend the elastin and allow dilatation. During dilation, levels of cytokines and hyaluronic acid begin to decrease, which may serve to decrease collagenolytic activity and allow the cervix to begin the process of repairing itself. Despite this advance knowledge of cervical ripening, the signals responsible for the initiation of these changes remain to be elucidated. If we can understand the exact mechanisms that affect these changes, then we may be better able to address such complex issues as cervical incompetence, preterm delivery, postterm delivery, and proper "ripening" of the cervix to avoid surgical delivery for arrest disorders of the active phase.