Uterine electrical activity, oxytocin and labor: translating electrical into mechanical

Uterine activity plays a crucial role in labor, especially when utero-tonic materials are administered. We aimed to determine the electrical responsiveness of the uterine musculature to labor augmentation with oxytocin using electrical uterine myography (EUM) technology, and to assess whether the kinetics of the EUM device may serve as a predictor for successful vaginal delivery.

EUM prospectively measured electrical uterine activity in women with singleton gestations at term (≥ 37 + 0 weeks) undergoing labor augmentation by oxytocin administration. The results were reported as the EUM index, which represented the mean electrical activity in 10-min intervals and measured in units of microwatt per second (mW/s). Measurements were performed at least 30 min before oxytocin initiation and until at least four contractions per 10 min were recorded by standard tocodynamometry. The delta EUM index was defined as the difference between the mean EUM index before and after the initiation of oxytocin.

The mean EUM index increased significantly during oxytocin augmentation in all the parturients (P < 0.001). Mean and minimum (but not maximum) uterine electrical activity during oxytocin infusion correlated with the baseline uterine activity. The delta EUM index was not significantly affected by demographic or obstetric parameters. There was no correlation between the delta EUM index and time to delivery or the mean EUM index during oxytocin administration and time to delivery.

Uterine electrical activity as evaluated by EUM is significantly intensified following oxytocin administration, regardless of obstetrical characteristics, and is correlated with the baseline uterine electrical activity prior to oxytocin infusion.