Objective: The objective of the study was to assess sonographic changes in cervical length and posterior cervical angle in women undergoing cervical ripening with an extraamniotic Foley catheter and to determine whether pre- and postripening ultrasound parameters could help predict successful cervical ripening and the outcome of labor induction.
Study design: Cervical length and posterior cervical angle were measured by transvaginal sonography in 155 women with a Bishop score of 4 or less before placement of a transcervical Foley catheter for cervical ripening. At the time of Foley removal, women who did not enter active labor underwent a second ultrasound assessment of the cervix. Outcome measures were successful ripening, vaginal delivery, vaginal delivery within 24 hours, and vaginal delivery achieved with the Foley only. Multiple logistic regression models were generated to identify pre- and postripening clinical and ultrasound parameters independently associated with successful induction.
Results: Forty patients (25.8%) went into active labor after spontaneous expulsion or removal of the Foley, without any additional intervention. A successful cervical ripening was obtained with the transcervical catheter in 46 women (29.6%). One hundred six women (68.4%) had vaginal delivery. No correlation was found among maternal body mass index, maternal age, clinical cervical dilatation, sonographic posterior cervical angle, and any of the outcomes of interest. Multiple logistic regression showed that preripening sonographic cervical length was an independent predictor of successful ripening (odds ratio [OR] 10.2, 95% confidence interval [CI] 3.6 to 28.5), vaginal delivery (OR 2.6, 95% CI 1.2 to 5.5), vaginal delivery achieved with only Foley (OR 17.2, 95% CI 3.9 to 76.2), and vaginal delivery within 24 hours (OR 3.3, 95% CI 1.5 to 7.3). In the subgroup of women who did not enter labor with the transcervical Foley, at the time of catheter removal, a significant change was found in sonographic cervical length (33.1 mm [12.2 to 54.1] vs 24.0 mm [7.6 to 42], P < .0001] and sonographic posterior cervical angle (110 degrees C [70-160] vs 137 degrees C [88-170], P < .0001), compared with preripening findings. Transvaginal ultrasound cervical length was the only postripening characteristic that independently predicted vaginal delivery (OR 3.5, 95% CI 1.3 to 9.1).
Conclusion: Transvaginal sonography seems a useful diagnostic tool to assess objectively the efficacy of the Foley catheter as ripening method and helps predict the likelihood of a successful induction of labor in individual women who require preinduction cervical ripening.