Transvaginal ultrasound measurement of the cervix is increasingly used for the prediction of preterm labor. In comparison to clinical vaginal examination, it has the advantages of being highly reproducible, with a low inter-observer variability, and of offering an evaluation of the entire cervical canal, including the internal os. The sensitivity and specificity of transvaginal ultrasound have been validated by several studies in women with symptoms of preterm labor, however its clinical applications and its limits have yet to be fully determined. It is likely to be of benefit in the management of multiple gestations, but it appears unlikely to be of use in low-risk pregnancies. Finally, whether it can be applied to estimate the risk of cervical incompetence, or to determine the need for cervical cerclage placement has not yet been determined by methodologically satisfactory clinical studies.