Changes in cervical resistance and collagen fluorescence during gestation in rats

During pregnancy the role of the cervix shifts between two opposing functio ns. Throughout most of gestation, the cervix is rigid and resists tension i n order to maintain the products of conception inside the uterus. At term, however, cervical function changes drastically in order to accommodate stre tch and delivery. The events that control cervical function are not known. The aim of this study was to characterize changes in cervical resistance an d collagen content during pregnancy in the rat. To determine the change in cervical resistance, nonpregnant and timed pregnant Sprague Dawley rats wer e sacrificed at various times. Their cervices were isolated and suspended i n organ baths connected to a cervimeter for measurement of the stretch-tens ion relationship. In a different group of animals, cervical collagen conten t was measured using light-induced fluorescence in nonpregnant and, longitu dinally, in pregnant rats. Cervical resistance and collagen content decreas ed progressively during pregnancy. The changes in cervical resistance mirro red those in cervical collagen content and the nadir in both occurred about two days prior to the onset of labor. Our study suggests that cervical pre paration for delivery does not occur acutely at the time of labor and that cervical collagen content determines cervical resistance.