The dimension of chaos in the fetal heart rate.

Variability in the fetal heart rate is known to be a sign of fetal well-being, and yet the origins of the variations remain unclear. This study incorporated the nonlinear analytic techniques of phase-space reconstruction and dimensional analysis to 12 normal heart rate tracings obtained from fetal scalp electrodes of fetuses in labor. Phase-space attractors were constructed with the method of time delays and showed characteristics consistent with those of nonlinear chaotic systems. Dimensional analysis resulted in three distinct groups being identified. Results indicate that control of the fetal heart rate may be modeled as a nonlinear or chaotic system, and analytic techniques borrowed from the physical sciences are useful in exploring heart rate variability. That different groups could be distinguished among qualitatively similar heart rate tracings may lead to understanding of discrepancies between evaluation of the monitor tracing and neonatal outcome.