Uterine Electrical Signals and Cervical Dilation During the First Stage of Labor

Objective: The purpose of this study was to explore the changes in uterine electrical signals recorded by electromyography in relationship with the progression of cervical dilation during the first stage of labor. Methods: Uterine electromyography was recorded from the abdominal surface for 30 min in 200 nulliparous women presenting at ≥ 370/7 weeks of gestation. Eight groups were defined as follows: Group 1 (n=10), non-laboring patients with no cervical effacement; Group 2 (n=15), patients with cervical effacement; Groups 3 to 7, patients in the first stage of labor with cervical dilation at 1–2 cm (n=10), 2–3 cm (n=50), 3–5 cm (n=45), 5–7 cm (n=30), and 7–9 cm (n=25), respectively; and Group 8 (n=15), patients in the second stage of labor with the cervix at 10 cm dilation. Uterine electromyography bursts were characterized by the analysis of various burst characteristics, including number of bursts, total power, and peak frequency of power density spectrum. Intergroup differences were assessed using one-way analysis of variance, and linear relationships between data were determined using Pearson’s correlation coefficient. Results: The burst frequency (number/30 minutes) and power density spectrum peak frequency increased steeply to peak levels at a cervical dilation of about 3 cm. However, the electromyography burst power reached peak levels at a cervical dilation of 5–7 cm. The correlations of the frequency of bursts (R=0.934, P<0.001), power (R=0.890, P<0.001), and power density spectrum peak frequency (R=0.972, P<0.001) with cervical changes were significant. Conclusions: Uterine electromyography effectively quantifies the contribution of uterine muscle electrical activity to the advancement of cervical dilation with the progression of labor. This study suggests that the dilation of the cervix is related to uterine electricity activity, helping to clarify the labor process.