A novel method for evaluating uterine cervical consistency using vaginal ultrasound gray-level histogram

Aims: To evaluate uterine cervical consistency using a vaginal ultrasound gray-level histogram. Methods: Vaginal ultrasound and digital examination were performed for 214 women with low-risk singleton pregnancy during 27-30(th) pregnancy week. The mean gray-level (MGL) of an ultrasound gray-level histogram, representing the echogenicity of a region of interest, was measured in the midsection of anterior and posterior cervical walls. The difference in MGL between anterior and posterior (AP difference) was related to the Bishop sub-score for cervical consistency (0, 1, or 2), determined before ultrasound. Results: A larger positive AP difference indicated significantly lower Bishop sub-score. After analyzing the receiver operator characteristic curves for the AP difference, a value of 1.42 and -1.98 was the best cut-off value to determine a hard cervix (score 0) and a soft cervix (score 2), respectively. To identify a hard cervix, this test had 71% sensitivity and 82% specificity. For a soft cervix, it was 66% and 87%, respectively. Conclusions: A more echogenic anterior than posterior cervix indicates a hard cervix; the greater the difference in echogenicity between anterior and posterior walls the harder the cervix. The difference in MGL of the ultrasound gray-level histogram may enable objective evaluation of cervical consistency.