Defining uterine tachysystole: how much is too much?

Am J Obstet Gynecol. 2012 Oct;207(4):290.e1-6. doi: 10.1016/j.ajog.2012.07.032. Epub 2012 Jul 31.


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.

MeSH terms

  • Adult
  • Female
  • Heart Rate, Fetal / drug effects*
  • Humans
  • Infant, Newborn
  • Labor, Induced / adverse effects*
  • Labor, Induced / methods
  • Misoprostol / adverse effects
  • Misoprostol / therapeutic use*
  • Oxytocics / adverse effects
  • Oxytocics / therapeutic use*
  • Pregnancy
  • Pregnancy Outcome
  • Prospective Studies
  • Uterine Contraction / drug effects*


  • Oxytocics
  • Misoprostol