Sonography and transfundal pressure in the evaluation of the cervix during pregnancy

Ultrasonographic evaluation of the cervix in pregnancy has provided some insight into premature delivery and pregnancy wastage. Its use has led to the development of cervical length nomograms in uncomplicated singleton pregnancies and to the realization that varying degrees of cervical incompetence exist. In some instances the internal os has been observed to dilate and funnel in the early second trimester while in others these changes occur gradually into the third trimester. Transient cervical changes have been linked to premature delivery and extended ultrasonographic inspection is required for their detection. Although sonography may allow the identification of women who deliver prematurely, it has not demonstrated enough discriminatory power to recommend its routine use for this purpose. Pre- and postoperative inspection of the cervix in elective and emergency cerclage procedures may become influential in outpatient management. A method of functional evaluation of the cervix using transfundal pressure (TFP) has been introduced which may lead to earlier diagnosis of cervical incompetence. The significance of descent of the membranes in response to TFP and sonographic findings consistent with premature cervical changes have not been validated because of surgical intervention performed in response to these findings. Our review concludes that, although sonography of the cervix may be useful in selective cases, more information on the natural history of abnormal cervical sonographic findings and controlled randomized trials are needed before recommendations on surgical intervention can be made.