Use of External Uterine Electromyography Across Stage I Labor

Introduction Highly sensitive, external uterine electromyography (EMG) measures myometrial electrical activity and is noninvasive compared with the clinical intrauterine pressure catheter. Most experimental studies have measured EMG in 30‐minute epochs, limiting the utility of this instrumentation in intrapartum clinical practice. To test proof of concept, surface uterine EMG contraction activity was continuously collected throughout the first stage of labor from healthy women at term gestation with (n = 3) and without (n = 1) epidural or combined spinal‐epidural analgesia for a maximal length of 11 hours and 24 minutes. Methods EMG activity was recorded concurrently with tocodynamometer (toco) signals, using a pair of electrodes on the left and right sides of the maternal umbilicus with grounds attached to both hips of the reclining woman in labor. The preamplifier cutoff frequency settings were appropriate to monitor smooth muscle contraction in labor, with the analog high‐pass filter set at 0.05 Hz and the low‐pass filter at 1.50 Hz. Signals were sampled at 100 Hz, transmitted to a computer, and visualized by Chart 4.2 software. EMG data from epochs at baseline, during the pre‐epidural fluid bolus and at the 60‐minute post‐epidural test dose, and at 3, 5, 6, and 8 cm dilatation were analyzed for burst power spectrum peak frequency (Hz), burst power spectrum amplitude (mV2), and burst duration (seconds). Results Uterine EMG contractile bursts were preceded and followed by a stable baseline and coincided with toco contractions. Movement artifacts were negligible, and large movement artifacts were easily distinguishable. The EMG bursts and toco contractions remained clearly identifiable, even when one woman without epidural analgesia stood beside the bed laboring for approximately 10 minutes. Burst spectral components fell within the expected 0.34‐to‐1.00 Hz range for term labor. Discussion High‐quality data demonstrate that EMG instrumentation effectively and accurately measures uterine contraction parameters across the first stage of term labor.