Analysis of cervical dynamics by ultrasound imaging.

Preterm birth is generally due to cervical ripening during the second trimester of pregnancy. The diagnosis of cervical incompetence is mostly based on the measurement of the shortened cervical length from transvaginal ultrasound (TVUS) images. We investigated the cervical dynamic response to spontaneous or imposed variations of intrauterine pressure, which may induce cervical shortening. The TVUS images of the cervix sagittal cross-sections were recorded from six women in mid pregnancy. The cervical dynamics was observed while the subject was either in a supine position, kneeling, or had undergone transfundal pressure in a supine position. Each subject was tested in all three positions, but the dynamic response was observed in only one of them. The time-dependent analysis was performed on consecutive TVUS images at time intervals of 1 s to extract the dynamic response of the funneling geometry and the closed cervical length. The internal os was considered as being a point on the uterine wall and characterized by a sharp gradient of the inner wall of the uterine cavity. Dynamic evaluation of TVUS images revealed that shortening of the cervical length was greater than 30% and that the funneling percentage was greater than 40%. This study demonstrates the clinical potential for dynamic assessment of cervical response due to excessive uterine pressure, in addition to its application for the conventional measurement of cervical length.