RESUMO
OBJECTIVE: During pregnancy, the stiffness of the cervical tissue decreases long before the cervical length decreases. Therefore, several approaches have been proposed in order to ensure a more objective assessment of cervical stiffness than that achieved by digital evaluation. Strain elastography has shown promising results. This technique is based on an ultrasound assessment of the tissue deformation that occurs when the examiner applies pressure on the tissue with the ultrasound probe. However, the results are only semi-quantitative as they depend on the unmeasured force used by the examiner. We, therefore, hypothesized that a force-measuring device applied to the handle of the ultrasound probe may render the technique quantitative. With this approach, the stiffness is the force (measured by the device) divided by the compression (measured by the elastography platform). One perspective is the early identification of women at risk of preterm birth in whom cervical stiffness may decrease long before cervical shortening. Another perspective is cervical evaluation when planning labor induction. In this feasibility study, we aimed to evaluate how quantitative strain elastography performs when a commercially available strain elastography platform (by which the algorithm is unavailable) is combined with a custom-made, force-measuring device. We studied how the assessments were associated with the gestational age in women with uncomplicated pregnancies and how they were associated with cervical dilatation time from 4 to 10 cm in women undergoing labor induction. METHODS: In the analysis, we included quantitative strain elastography assessments from 47 women with uncomplicated singleton pregnancies, with gestational age between 12+0 and 40+0, and from 27 singleton term-pregnant women undergoing labor induction. The force-measuring device was mounted on the handle of a transvaginal probe. The strain values (i.e. the compression of the cervical tissue) were obtained by the elastography software of the ultrasound scanner (GE Voluson E10). The region of interest was placed within the central part of the anterior cervical lip. Based on the force data and strain values, we calculated the outcomes cervical elastography indexGE (CEIGE) and the cervical strength indexGE (CEIGE x cervical length: CSIGE). RESULTS: The average CEIGE was 0.24 N at week 12 and 0.15 N at week 30-34. For CSIGE these figures were 8.2 and 4.7 N mm, respectively (p = 0.002). Among women undergoing labor induction, the CEIGE was associated with a cervical dilatation time (4-10 cm) beyond 7 h. For nulliparous women, this area under the ROC curve was 0.94. CONCLUSION: Quantitative strain elastography may constitute a tool for the evaluation of a uterine cervix with normal length in women at risk of preterm birth and in women undergoing labor induction. The performance of this tool deserves evaluation in larger clinical trials.
