(750) The Effect of the ARRIVE Trial on Nulliparous Term Singleton Vertex (NTSV) Cesarean Birth Rate

Objective: The ARRIVE trial showed lower cesarean birth rates with labor induction at ≥39 weeks among low-risk nulliparas. These findings lowered the threshold for labor induction across all pregnant people, but little is known regarding the effects on nulliparous term (≥37 weeks) singleton vertex (NTSV) cesarean birth rate. Thus, we sought to determine how the cesarean birth rate among all NTSV pregnancies has changed after the ARRIVE trial.

Study Design: We conducted a population-based, cohort study of all NTSV (≥37 weeks), non-anomalous births using data from the US Natality database. The pre-ARRIVE group included births between Jan-2015 and Dec-2017 and the post-ARRIVE group included births between Jan-2019 and Dec-2021. We compared the mean NTSV cesarean birth rate between both groups. Multivariable logistic regression was performed to adjust for clinical differences. A logistic regression model was used to project the NTSV cesarean birth rate over time based on the pre-ARRIVE rate and compare the rates, per year, using Wald confidence intervals.

Results: There were 3,611,386 births in the pre-ARRIVE group, and 3,447,887 in the post-ARRIVE group. The NTSV cesarean birth rates pre- and post-ARRIVE were 25.8% and 25.9%, respectively. After adjusting for clinical differences between the groups, there was a decrease in the NTSV cesarean birth rate post-ARRIVE (adjusted odds ratio (aOR) 0.91, 95% confidence interval (CI) 0.908- 0.915). The NTSV cesarean birth rates (both observed and projected) are summarized in Figure 1. The absolute NTSV cesarean birth rate post-ARRIVE remained lower compared to the projected rate based on pre-ARRIVE trends (p< 0.05).

Conclusion: Despite a lower than projected rate of NTSV cesarean birth, the overall rate continued to increase. This rate increase warrants further investigation into the effects of the ARRIVE trial findings on populations outside the ARRIVE’s inclusion criteria.