Multifractility in labor contraction dynamics

Recently, we presented evidence that electromyographic signals during healthy uterine contractions may have a fractal temporal structure [M. Sabry-Rizk et al., Transactions of the Institute of Measurement and Control, Vol. 22, No. 3, p. 243-70, 2000]. We also uncovered a loss of chaoticity in very early segments of uterine contractions for typical cases of failure to progress in the first stage of labor and ending with surgical procedure (Caesarean section). In both healthy and unhealthy labor contractions, quadratic Volterra structures were used to estimate non-linearity in their respective measured time series. Healthy uterine contractions start from the 16^th week of the human pregnancy. These contractions become more and more frequent and increase in strength up to the end of pregnancy. In this paper, we use the Hurst analysis algorithm to detect fractility in abdominal electromyographic signals (AEMG), and show that the multi-fractal character and nonlinear properties of the healthy contractions are encoded in the Fourier phases. Results are shown for representatives of the following groups: (i) healthy pregnancy, spontaneous labor and parturition, and (ii) full term at 40 weeks, prolonged labor (arbitrarily defined as lasting more than 12 hours) and ending with Caesarean section. Our ongoing study is aimed at exploiting the aforementioned method to characterize potentially pre-term labor (less than 37 weeks) by analyzing electromyographic signals as early as 16 weeks gestation.