228 Medical resource use in 39 weeks elective induction versus expectant management: stratified by bishop score

Abstract

To determine if there is an interaction between Bishop score and use of resources between elective induction of labor (IOL) vs. expectant management (EM) at ≥ 39 weeks. Secondary analysis of a RCT of IOL at 39 0/7-39 4/7 weeks compared with EM in low-risk nulliparous pregnancies. The primary outcome of this analysis was maternal hospital length of stay from admission until discharge. Antepartum, intrapartum, postpartum, and neonatal resources were defined a priori in the parent trial. The interaction between group assignment (IOL vs. EM) and cervical status was evaluated for antepartum resources using the modified Bishop score at randomization, and for intrapartum, postpartum, and neonatal resources using the modified Bishop score at presentation for delivery. Multivariable generalized linear modeling and modified Poisson regression were performed. Due to multiple comparisons 99% confidence intervals were calculated (statistical significance, p < 0.01). Of 6,094 patients with data available, 3,059 were randomized to IOL and 3,035 to EM. There were no differences in baseline characteristics between the two groups, including Bishop score at randomization. However, participants assigned to EM had higher Bishop scores at presentation for delivery (median, IQR: 7 (5-8) vs. 5 (4-7), p<0.001) compared with those assigned to IOL. There were no significant interactions between cervical status and primary or secondary outcomes except use of cervical ripening (p-value for interaction <0.001). After adjustment for confounders, patients in the IOL group were nearly 3 times as likely to undergo cervical ripening than the EM group if their Bishop score was ≥5 (aRR 2.81, 99% CI 2.35-3.36,) but had only a 24% increased likelihood of cervical ripening if the Bishop score was <5 (aRR 1.24, 99% CI 1.08 - 1.43). Aside from cervical ripening, the difference in resource utilization between the elective induction and expectant management groups is not modified by Bishop score. The Bishop score should not alter the counseling regarding the use of resources for labor induction after 39 weeks.