Uterine tachysystole in spontaneous labor at term

Objectives: The objective of this study is to determine the incidence of uterine tachysystole and its association with spontaneous labor at term.

Methods: A retrospective cohort study of 8008 women in spontaneous labor (without prostaglandins or oxytocin). Fetal heart tracings and uterine activity were recorded every 15 min.

Primary outcome: occurrence of tachysystole (> 5 uterine contractions /10 min over 30 min periods).

Secondary outcomes: non-reassuring fetal heart tracings (NRFHT), NICU admissions, and cesarean deliveries.

Results: About 890 patients (11.1 %) had at least one episode of tachysystole. Non-whites have higher incidence of uterine tachysystole; adjusted odds ratio (aOR) was 1.66 for Hispanics (95% CI 1.28-2.05), 1.58 for African Americans (95% CI 1.05-2.38), and 1.51 for Asians (95% CI = 1.13-2.0). The use of epidural analgesia was higher in the tachysystole group (62.2% versus 40.9%, aOR 1.89, CI 1.58-2.26; p < 0.001). Tachysystole was more frequent among nulliparous women and in women carrying higher weight fetuses. Oligohydramnios (aOR 1.62, CI 0.70-3.72; p < 0.004), and NRFHT were more common in the tachysystole group (4.2% versus 2.5%, p = 0.002). Newborns in the tachysystole group were two times more likely to be admitted to NICU (30 /890 [3.4%] versus 122 /7118 [1.7%], OR = 2, p=0.001). There was no difference in the frequency of meconium-stained amniotic fluid or Apgar scores <7 at 5 min.

Conclusion: Uterine tachysystole occurs in more than 10% of spontaneous labors and is associated with NRFHR, increased rate of caesarean deliveries and NICU admissions. It is not associated with low Apgar scores or meconium-stained amniotic fluid.