Defining uterine tachysystole: How much is too much?

Objective: We sought to determine if uterine tachysystole, <6 contractions per 10 minutes, within the first 4 hours of labor induction, is associated with adverse infant outcomes. Study Design: This was a prospective cohort study of 584 women <37 weeks' gestation undergoing induction of labor with 100 μg of oral misoprostol. Fetal heart rate tracings were analyzed for contractions per 10 minutes during the initial 4 hours after misoprostol administration. Patients were analyzed based on the maximum number of contractions per 10 minutes. Infant condition at birth was assessed using the fetal vulnerability composite. Results: Adverse infant outcomes showed no association with increasing number of contractions per 10 minutes. Six or more contractions in 10 minutes were significantly associated with fetal heart rate decelerations (P ≤.001). Analysis was performed using the maximum number of contractions per 30 minutes with similar results. Conclusion: Uterine tachysystole, as currently defined, when occurring remote from delivery is not associated with adverse infant outcomes.