Evaluation of cervical stiffness during pregnancy using semiquantitative ultrasound elastography

Objective To evaluate cervical stiffness during pregnancy using ultrasound-derived elastography, a method used to estimate the average tissue displacement (strain) within a defined region of interest when oscillatory compression is applied. Methods Strain was calculated in two regions of interest, the endocervical canal and the entire cervix, from three anatomical planes of the cervix: mid-sagittal in the plane used for cervical length measurement and in cross-sectional planes located at the internal and external cervical os. Associations between strain values, method of ascertainment and patient characteristics were assessed using linear mixed models to account for within-subject correlation. Inter-rater agreement in defining the degree of cervical stiffness was evaluated in 120 regions of interest acquired by two operators in 20 patients. Results A total of 1557 strain estimations were performed in 262 patients at 840weeks of gestation. Adjusting for other sources of variation, (1) cervical tissue strain estimates obtained in the endocervical canal were on average 33% greater than those obtained in the entire cervix; (2) measurements obtained in the cross-sectional plane of the external cervical os and sagittal plane were 45% and 13% greater than those measured in the cross-sectional plane of the internal cervical os, respectively; (3) mean strain rates were 14% and 5% greater among parous women with and without a history of preterm delivery compared with those of nulliparous women, respectively, and were on average 13% greater among women with a cervical length of between 25 and 30mm compared to those with a cervical length of>30mm; and (4) cervical tissue strain was more strongly associated with cervical length than with gestational age. Conclusion Semiquantitative elastography can be employed to evaluate changes in cervical stiffness during pregnancy.