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.