Time of day of induction impacts the total duration of labor

BACKGROUND: Spontaneous labor onset peaks during the late evening and early morning hours, indicating a circadian influence on parturition. However, the effect of the time of day of labor induction on labor duration and obstetrical outcomes remains unexplored. We hypothesize that the time of day of labor induction affects induction of labor duration and the risk of cesarean delivery. OBJECTIVE: This study aimed to determine whether the time of day of labor induction impacts induction of labor duration and delivery outcomes in term pregnancies, and whether maternal characteristics such as body mass index and parity modulate this effect. STUDY DESIGN: This retrospective cohort study analyzed 3363 term pregnant participants who underwent induction at a single US hospital between 2019 and 2022. Time of induction was defined as the time of administration of the first cervical ripening agent or synthetic oxytocin (ie, Pitocin). Induction of labor duration was calculated as the time from induction to delivery. Multivariable analyses, survival models, and circadian rhythm analyses were performed to evaluate associations between time of day of labor induction, induction of labor duration, cesarean delivery, and neonatal outcomes. RESULTS: Induction of labor duration followed a significant circadian rhythm (P