Excessive uterine activity accompanying induced labor

Objective: To estimate the incidence and timing of excessive uterine activity accompanying induction of labor with misoprostol using different routes (oral or vaginal) and forms (intact tablet or crushed) and to compare these with dinoprostone gel, oxytocin, and spontaneous labor. Methods: This retrospective cohort study included 519 women at term who had labor induced and 86 women at term in spontaneous labor. Induction agents included misoprostol, dinoprostone, or oxytocin. Fetal heart rate and uterine activity tracings were analyzed independently by three maternal-fetal medicine physicians. The diagnosis of tachysystole or hyperstimulation required the agreement of two or more reviewers. Results: The incidence of tachysystole was highest with misoprostol administered by vaginal tablet (misoprostol vaginal tablet 50 μg every 4 hours, 48.6%; vaginal tablet crushed 50 μg and suspended in hydroxyethyl gel every 4 hours, 30.7%, P = .009; oral tablet 50 μg every 4 hours, 22.2%, P = .001; oral tablet crushed 50 μg every 4 hours, 15.5%, P < .001; dinoprostone gel, 33.0%, P = .022; intravenous oxytocin, 30.2%, P = .027; and spontaneous onset of labor, 23.3%, P < .001). Hyperstimulation occurred more often with dinoprostone gel (16.5%) than with other forms of induction or spontaneous labor. Hyperstimulation occurred significantly more often with vaginal misoprostol crushed tablet (7.9%) and vaginal misoprostol intact tablet (7.6%) than with crushed oral misoprostol (1.0%) (P = .016 and .018, respectively). There was a shorter time to tachysystole with increasing doses of vaginal misoprostol tablet (P = .01). Conclusion: The incidence of tachysystole and hyperstimulation, and time to tachysystole, varied depending on the route and form of misoprostol given.