(127) Among patients undergoing induction who reach active phase, does prolonged latent phase matter?

Objective: While guidelines exist for diagnosing a failed induction of labor (IOL), there is little data assessing the impact of a prolonged, but not failed, latent phase on the remainder of the IOL trajectory. Therefore, we sought to assess if a prolonged latent phase is associated with an increased risk of Cesarean delivery (CD) or labor arrest among patients undergoing IOL.

Study Design: This was a secondary analysis of a large prospective cohort study of term, singleton inductions with intact membranes and an unfavorable cervix at 2 sites from 2018-2022. Only patients who reached active phase (defined as ≥6cm dilation) were included. Prolonged latent phase was defined as < 6 cm dilation after ≥12 hours with ruptured membranes and receiving oxytocin infusion. The primary outcome was CD for any indication. Generalized estimating equations were used to calculate relative risk (RR) and adjust for confounders.

Results: Of 8,509 patients in the cohort, 7,451 (87.6%) reached active phase and were included. 472 (6.3%) had a prolonged latent phase with demographic and clinical characteristic differences noted in the Table. There was a higher rate of CD for those with a prolonged latent phase compared to those without, which remained after adjusting for BMI, insurance type, diabetes, and Bishop score at the start of IOL (25.2% vs 9.9%, p< 0.001, aRR 1.69 95%CI [1.41-2.01]). This increased risk was noted among nulliparous patients (27.8% vs. 14.3%, p< 0.001, aRR 1.67 95%CI [1.39-2.00]) but not multiparous patients (8.1% vs. 3.2%, p=0.03, aRR 2.13 95%CI [0.88-5.12]). In those with a CD, there was a higher rate of CD for labor arrest among patients with prolonged latent phase compared to those without (19.5% vs. 6.3%, p< 0.001), with an increased risk of CD for labor arrest noted among nulliparous (21.7% v. 9.4%, p< 0.001), but not multiparous patients (4.8% v. 1.5%, p=0.07).

Conclusion: While the majority of patients with a prolonged latent phase of labor ultimately have a vaginal delivery, it is an independent risk factor for CD in active phase, both overall and among nulliparous patients.