Favorable Simplified Bishop Score after cervical ripening associated with decreased cesarean birth rate.

BACKGROUND

A favorable Simplified Bishop Score (>5) before the induction of labor is associated with successful vaginal birth. Patients with an unfavorable Simplified Bishop Score (≤5) undergo cervical ripening before the administration of oxytocin. However, data are limited regarding the utility of the Simplified Bishop Score after cervical ripening.

OBJECTIVE

The objective of this study was to determine if the Simplified Bishop Score before oxytocin induction but after cervical ripening is associated with cesarean delivery.

STUDY

DESIGN

We conducted a retrospective cohort study on patients undergoing induction of labor from the Consortium on Safe Labor. The patients with a singleton term pregnancy who initially underwent cervical ripening were included. Those with a history of cesarean delivery were excluded. The outcomes of patients with a favorable Simplified Bishop Score after cervical ripening were compared with those with an unfavorable Simplified Bishop Score. The primary outcome was the mode of birth. A log-binomial regression was performed to calculate the relative risk and control for confounders such as admission Simplified Bishop Score and parity.

RESULTS

A total of 5807 patients met the criteria to be included in the study. 4235 (73%) patients had a favorable cervix, and 1572 (27%) patients had an unfavorable cervix after cervical ripening. The favorable group had a decreased rate of cesarean delivery than the unfavorable group (risk ratio, 0.35; 95% confidence interval, 0.30-0.40). Both the groups had low rates of maternal chorioamnionitis, though the patients with an unfavorable cervix were at a higher risk. There was no significant difference in the rates of postpartum hemorrhage or neonatal intensive care unit admission. Lower rates of cesarean delivery among the favorable group persisted when stratifying by parity (nulliparous: risk ratio, 0.37; 95% confidence interval, 0.31-0.43; multiparous: risk ratio, 0.22; 95% confidence interval, 0.14-0.36). After controlling for maternal age, prepregnancy body mass index, parity, gestational age, and Simplified Bishop Score at admission, a favorable cervix remained significantly associated with fewer cesarean births (risk ratio, 0.55; 95% confidence interval, 0.46-0.66).

CONCLUSION

In women undergoing labor induction, a favorable Simplified Bishop Score after cervical ripening and before the start of oxytocin is associated with a decreased rate of cesarean delivery, even after adjusting for parity and Simplified Bishop Score at admission. Moreover, the Simplified Bishop Score assigned after cervical ripening could be used to inform the timing of oxytocin initiation. However, further research is necessary to determine the ideal endpoint of cervical ripening.