Abstract
The Lyapunov dimension allows for observation of the complexity and temporal dynamics of chaotic systems. Here, we examined the changes in the Lyapunov dimensions of the heart sounds of human mother-fetus pairs from early pregnancy to after birth. Time-series data of the heart sounds of four pregnant women and their fetuses were obtained at four phases (early, mid, and late pregnancy, and the early postnatal period) under five different vocal stimulation conditions (no stimulation, during and after stimulation with a recording of the mother′s voice, and during and after stimulation with a recording of a stranger′s voice), and the medium Lyapunov dimension for each mother and fetus at each phase and under each stimulation condition was determined. The Lyapunov dimension of the mother did not significantly change from early pregnancy to the postnatal period. In contrast, that of the fetus increased dramatically at each gestation phase (p<0.001) until it matched that of the mother during the postnatal period. These findings imply that mothers maintain a mature chaotic state throughout pregnancy whereas fetuses harbor a changing, more complex chaotic state.
