A Dual Mechanism of Biomechanical Change in Rat Cervix in Gestation and Postpartum: Applied Vascular Mechanics

Biomechanical studies were designed to determine the dynamic progression of the uterine cervix of pregnant rats at various stages of gestation and to determine its functions in retaining the fetus while at the same time undergoing characteristic softening to allow for dilatation at parturition. Whole cervices from Sprague-Dawley rats at 10, 15, and 21 days gestation and at 3 days postpartum were subjected to detailed biomechanical studies. Tension–length change, tension–diameter, pressure–area, stress–diameter, and stress–strain curves were calculated using analytical methods adopted from vascular mechanics. The circular diameter of the tissue was greatly increased as pregnancy advanced. Cervix volume increased, while tissue wall stress and cervix pressure were both maintained in a constant range throughout pregnancy. The compliance increased until term. The rat cervix undergoes two mechanical changes, a change in mechanical properties and a increase in volume, that allow it to maintain its two physiological functions of: (a) softening in preparation for delivery, and (b) at the same time remaining undilated in order to maintain fetuses in utero.