Nonlinear dynamic tools for characterizing abdominal electromyographic signals before and during labour

Abstract

This paper presents evidence that electromyographic signals during healthy uterine contractions may have a fractal temporal structure. Healthy uterine contractions start from the 16th week of the human pregnancy. These contractions become more and more frequent and increase in strength up to the end of pregnancy. Here we investigate the possibility that time series generated by labour physiological control systems may be members of a special class of complex processes which are noise driven and may require more than one exponent to characterize their fractal scaling properties. We use a simplified version of the Hurst analysis algorithm to detect fractility in abdominal electromyographic signals (AEMG) and quadratic Volterra structures to estimate nonlinearity in them. We uncover a loss of chaoticity in very early segments of uterine contractions for typical cases of failure to progress in the first stage of labour and ending with surgical procedure (Caesarean section). Results are shown for representatives of the following groups: (1) healthy pregnancy, spontaneous labour and parturition, (2) full term at 40 weeks, prolonged labour (arbitrarily defined as lasting more than 12 h) and ending with Caesarean delivery, and (3) preterm spontaneous labour (less than 37 weeks).