Outcomes After Internal Versus External Tocodynamometry for Monitoring Labor

Abstract

Professional societies in obstetrics and gynecology have recommended the use of internal tocodynamometry to monitor uterine contractions during induction or augmentation of labor. This recommendation is based on the hypothesis that internal tocodynamometry in comparison to external monitoring provides a more accurate assessment of contractions and may quantify the frequency, duration, and magnitude of uterine activity more accurately. Monitoring with internal tocodynamometry may improve maternal and fetal outcomes by allowing better adjustment of oxytocin, thereby preventing uterine hyperstimulation and fetal hypoxia. Because limited clinical data support such hypotheses, the recommendations are based on expert opinion. This randomized, multicenter, controlled clinical trial was designed to evaluate whether the use of internal tocodynamometry during labor, in a population of women with an indication for induced or augmented labor, provides superior outcomes compared to use of external monitoring. The study subjects were 1456 singleton women at >36 weeks' gestation, who required either induction or augmented labor with intravenous oxytocin. The women were randomly assigned to either an internal tocodynamometry group (n = 734) or an external monitoring group (n = 722). The trial was performed at 6 hospitals in the Netherlands between 2004 and 2007. The composite primary outcome was the rate of operative delivery, including cesarean section or instrumented vaginal delivery. Secondary outcomes evaluated were the use of antibiotics during labor, time from randomization to delivery, and adverse neonatal outcomes defined as a 5-minute Apgar score below 7, an umbilical artery pH below 7.05, or a neonatal admission longer than 48 hours. Operative delivery was performed in 230 (31.3%) of the women in the internal-tocodynamometry group and in 214 (29.6%) of those in the external-monitoring group (relative risk with internal monitoring = 1.1; 95% confidence interval = 0.91-1.2). No significant difference was found between the 2 groups in the frequencies of secondary outcomes. The rate of adverse neonatal outcomes was also similar (14.3% with internal monitoring vs. 15.0% with external monitoring; relative risk = 0.95, 95% confidence interval = 0.74-1.2). The use of the intrauterine pressure catheter was not associated with serious adverse events. These findings show no significant difference in the rates of operative delivery or adverse neonatal outcomes between internal tocodynamometry and external monitoring of uterine contractions in a population of women with an indication for induction or labor augmentation with oxytocin. The data do not support the routine use of internal tocodynamometry for monitoring contractions in women with induced or augmented labor.