The quantitative and objective assessment of cervical stiffness has great potential for the estimation of pre-term delivery risk, as well as for the prediction of the success of labor induction. Various methods can be used in vivo for cervical assessment such as vaginal digital examination or static elastography but to our knowledge, none of them can provide a quantitative, absolute and independent evaluation of cervical stiffness in vivo. In this study, such values were obtained in pregnant patients in vivo by using Supersonic shear Imaging technique (SSI). The stiffness of the lower anterior part of the cervix was quantified over a  8 mm region of interest, during vaginal ultrasound examination in 163 pregnant women. We were able i) to assess the range of normal elasticity values throughout the pregnancy, ii) to demonstrate the intra and interoperator reproducibility of the measurement and iii) to evaluate the potential of SSI for the discrimination of pre-term labour. The elastic modulus of the cervix was found to decrease significantly throughout the pregnancy. This study provides for the first time a database for absolute elastic modulus values of the cervix throughout the pregnancy. Stiffness was observed to decrease with gestional age, which is consistent with results previously obtained using a cervicotonometer. Cervical stiffness is reduced in patients diagnosed with pre-term labour.