ObjectiveAt the end of pregnancy, during the ripening process, the cervix changes its biochemical composition and structure to permit delivery. Recent research has proposed that these structural alterations may be due to changes in the water content of the extra cellular matrix ( ECM ) , alterations in the proteoglycan content, and/or changes in the activity of collagenases. MMPs are suspected to contributed to overall tissue remodeling in the uterus, the fetal membranes, and in the cervix during pregnancy. MMP - 8 and MMP - 9 concentrations have been shown to increase in the lower uterine segment during labor in parallel with changes in cervical dilatation. However, the exact MMPs and TIMPs that are present in the human cervix in pregnancy, and the mechanism by which their activity is controlled in cervical ripening are not fully understood.As we all know that diazepam is capable of inducing human cervical ripening. But the mechanisms how diazepam is involved in the ripening process and how it interacts with other mediators of cervical ripening remain unclear. Since the cervix undergoes a remodeling process before the onset of both term and pre-term partiturition that is characterized by decreased tensile strength and a change in texture, moreover, now the study of cervical ripening has been limited largely to animal models because of safety concerns that are related to tissue sampling during human pregnancy. So we measured the cervical tensile strength by cervical creep method and investigated the expression of MMP - 9/TIMP - 1 protein in the pregnancy rat cervix during normal pregnancy and in response to diazepam administration to determine whether MMP -9/TIMP - 1 expression is involved in the cervical ripening process.MethodsThe Wistar rats were obtained from the Second Affiliated Hospital Animal Lab of the Chinese Medical University. The day after mating was considered day of gestation in the presence of a vaginal plug. Animals that were used to study diazepam - induced cervical ripening were pretreated with different dose. Animals were killed on gestational days 13,16,20 and 21. The cervix was separated from the uterus;care was taken to exclude the more muscular protein above the mainly fibrous cervix. The tissue was rinsed in normal saline solution then used for measuring the cervical tensile strength or frozen in liquid nitrogen and stored at -