Digital filtering and fetal heart rate variability

The use of fetal monitoring during both the antepartum and intrapartum periods has become widespread. While it is generally agreed that fetal heart rate variability is an important indicator of fetal state, attempts to quantitatively evaluate fetal heart variability have been largely unsuccessful. This paper will review the problems of fetal monitoring and the proposed indicators of heart rate variability. It will be shown that through time series analysis we can not only explain the mathematical difficulties in monitoring heart rate variability but also understand the problems of the proposed indicators. Digital filters will be shown to be useful in obtaining true variability from the monitored data and in constructing useful indicators of fetal heart rate variability.