Tachysystole and risk of cesarean section after labor induction using misoprostol: a cohort study

Abstract Background In western countries, induction of labor is a common obstetrical intervention. Uterine tachysystole frequently manifests after cervical ripening by misoprostol vaginal inserts. Currently, there is insufficient evidence regarding the clinical impact of tachysystole during induction of labor. Therefore, the objective of the current study is to examine if tachysystole is associated with an increased risk of cesarean section following induction of labor by misoprostol vaginal inserts. Methods We conducted a retrospective cohort study of 446 women over 37 weeks of gestation admitted for labor induction by misoprostol vaginal inserts between May 2016 and May 2017. Fetal heart rate and uterine activity tracings were assessed for tachysystole, defined as ≥ 6 contractions per 10 minutes, averaged over a 30-minute window. Univariate analysis was performed by using t-test and Chi-square, comparing demographics, pregnancy characteristics, intrapartum monitoring, mode of delivery, neonatal outcomes (Apgar score < 7 at 5 minutes, umbilical cord artery pH < 7.10, neonatal intensive care unit admission) and maternal outcomes, with regard to the presence of tachysystole. The association between tachysystole and cesarean section was evaluated after adjusting for potential confounders by a modified Poisson regression model, expressed as an adjusted risk ratio and 95% confidence intervals. Results A total of 140 women (31.4%) presented with tachysystole. The median duration of tachysystole was 2 hours 12 minutes. The rate of cesarean section was 25.0% (N=35) among patients with tachysystole and 19.6% (N=60) for those without tachysystole. Presence of tachysystole during induction of labor with misoprostol vaginal inserts was not associated with cesarean section (adjusted risk ratio,1.0; 95% confidence interval, 0.7 to 1.4). Neonatal and maternal outcomes were similar between mothers who did and did not experience tachysystole. Conclusions This study illustrates that tachysystole is not associated with an increased risk of cesarean section after induction of labor by misoprostol vaginal inserts. The impact of excessive uterine activity on the fetal wellbeing defined by the frequency of uterine contraction alone is probably insufficient. Further research on the development of accurate measures of uterine contractility is necessary to better understand its effect on fetal well-being.