Conventional versus modified application of COOK Cervical Ripening Balloon for induction of labor at term: a randomized controlled trial

Background This study aims to evaluate the efficacy and safety of the modified application of COOK Cervical Ripening Balloon (CCRB) for induction of labor (IOL) at term in primipara. Methods A total of 227 singleton full-term pregnancies with indications of IOL were enrolled and randomly divided into the control and study groups in our hospital from January 2021 to December 2021. In the control group, a conventional method was used. Both the uterine and vaginal balloons were filled to 80 mL and removed after 12 h. In the study group, a modified method was used. The uterine and vaginal balloons were filled to 120 mL and 40 mL respectively. Light traction was given to help CCRB to be discharged after 12 h placement. Oxytocin was administered in both groups after CCRB was discharged before labor starting. The improved Bishop scores, duration of labor, and spontaneous delivery rate were evaluated in the two groups. Results The improved Bishop scores in the study group were 3.06 ± 0.97 at 12 h placement of CCRB and 4.37 ± 0.87 when CCRB was discharged, which were significantly higher compared to the control group (2.52 ± 0.79, p < 0.05). Duration of the first stage of labor and the full labor in the study group were significantly shorter than those in the control group ((6.17 ± 2.85) h vs. (7.27 ± 2.90) h, p = 0.010; (7.07 ± 3.18) h vs. (8.09 ± 3.11) h, p = 0.028). No difference in spontaneous delivery rate between the two groups was observed. But the delivery rate within 24 h between the two groups was significantly different (79.79% vs. 55.91%, p < 0.05). For the cases with initial Bishop scores ≤ 3, the improved score was significantly increased, the first stage of labor and the full labor were significantly shorter in the study group than those in the control group ( p < 0.05). Those results were not observed in cases with initial Bishop scores of 4–6. Conclusions The modified application of CCRB could benefit cervical ripening, shorten the duration of labor, especially for cases with poor cervical maturity, and improve the delivery rate within 24 h. Trial registration Retrospectively registered: ChiCTR2200058270. Registered 04/04/2022.