Simultaneous Measurement of Electrical Activity of Uterine, Abdominal and Pelvic Floor Muscles during the Second and Third Stages of Labor

Abstract

Background: The simultaneous recording of electrical activity (EA), responsible for the contractility of Uterine musculature (UT), Abdominal musculature (AB), and Pelvic Floor Muscles (PFM) during human parturition has not previously been studied. Activities of the muscle groups and their interactions are not completely understood during the final steps in parturition. This study describes the relationship between the muscle groups involved in delivery and contributes to a better understanding of their role and function. Objective: The aim of this novel observational study was to investigate the relationship of UT, AB, and PFM EA characteristics involved in the second stage of labor and delivery using electromyography (EMG) and examine the differences in EA characteristics between parous and nulliparous parturients. Study Design: This observational study included 28 women with term pregnancies in labor undergoing spontaneous delivery at a university-based hospital. PFM EA was recorded from the perineal surface, and simultaneous UT and AB EA were obtained from the abdominal surface using PowerLab hardware & LabChart software (ADInstruments, New South Wales, Australia). Each muscle grouping was electrically filtered based on previously established frequency characteristics. The detailed EA characteristics of the muscles were quantified during four phases of labor during uterine contractions and: 1) control Valsalva, known to elevate PFM EA above baseline; 2) maternal pushing efforts; 3) during delivery, and 4) the third stage immediately post fetal delivery before placental delivery. EA characteristics consisted of total power, peak power density spectrum (PDS), route mean squared (RMS), and EA duration and were further analyzed based on parity. Data was analyzed using Wilcoxon signed-rank test and Friedman's Two-Way Analysis of Variance by Ranks with SPSS software. Results: Visual inspection of EMG recordings show increasing EA during delivery and the third stage of labor compared to control Valsalva and second stage of labor. These observations are confirmed by statistical analysis of EMG records of all muscle groups' EA and clearly demonstrate substantial increases during delivery. There are statistically significant increases in the UT total power (p= 0.001), electrical burst length (p=0.014) and maximum RMS (p= 0.002), the AB total power (p= 0.002), RMS (p= 0.002) and PFM: total power (p= 0.001), electrical burst length (p= 0.010) and RMS (p= 0.010) between the measured intervals. The PDS did not vary significantly (p=>0.05) across any measured phases or muscle groupings. Multiparous parturients exemplified greater UT burst length (p=0.01) and PFM power (p=0.03). Nulliparous parturients showed greater UT PDS (p=0.02), AB PDS (p= 0.04), PFM and AB burst length (p= 0.03 and p=0.04, respectively) and AB power (p=0.02). Overall, the EA of muscles involved in delivery increases greatly during the expulsion of the fetus, indicating active involvement and the EA of PFM vary significantly and increase during the studied intervals. Conclusion: These studies provide a better understanding of the role of muscles involved in the process of the second and third stages of labor. 1) Fetal head distension of the PFM may contribute to stretch-induced EA and resultant increase in PFM resistance to delivery of the fetus. 2) Childbirth muscular processes results from the coordinated uterine and abdominal forces that must overcome the resistance of PFM. 3) Contractility of the PFM contributes to normal labor processes and deserves further investigation.