Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes

Objective: Limited data exist regarding uterine contraction intensity prior to membrane rupture. Using a novel technique of electrical uterine myography (EUM) we aimed to determine which factors affect myometrial activity during active phase of labor. Methods: EUM was prospectively measured in 37 women with singleton pregnancy at term during the active phase of labor until membranes' rupture. EUM was measured using non-invasive nine channels recorder with an EMG amplifier and three-dimensional position sensor. Uterine electrical activity was quantified with the EUM-index, defined as the mean electrical activity of the uterine muscle over a period of 10 min and measured in units of micro-Joule (microwatt per second [mW/s]). Results: The mean EUM-index at the first 10 min of the measurement was 3.3 ± 0.6 mW/s. In a stepwise linear regression model accounting potential confounders EUM was significantly affected by cervical dilatation (p = 0.005), maternal age (p = 0.04) and previous cesarean delivery status (p = 0.02). In a repeated measurement assessment of non-parametric Fridman's test for all subjects who had at least 10 continuouss EUM measurements, there was a significant increase in electrical uterine activity as labor progressed (p = 0.01). Conclusion: Electrical uterine activity during the active phase of labor prior to rupture of membranes is affected by maternal age, previous cesarean delivery status and cervical dilatation. Moreover, electrical uterine activity is enhanced throughout labor.