Interest of HI-RTE Elasticity in Obstetric

In obstetric, the investigators can't predict accurately with current means (BISHOP score, traditional cervix ultrasonography and fibronectin) the childbirth time and delay. If ultrasonography can determine the length, the cervix opening, it can't define its flexibility. Indeed, the conventional cervix ultrasonography can't inform us about the consistency of the uterine cervix. The elastography (elasticity imagery) is an innovating technology. It is a new technology currently used as part of breast cancer estimate. This diagnosis mean use the ultrasonography to measure the tissues answer under pressure. Its contribution in obstetric must be estimated to improve patients minimum fare. The main target of the investigators study is to estimate the interest of the measure of cervix elasticity degree by elastography in prediction of premature birth within a population of pregnant women