  Recently, multiple time scale characteristics of heart dynamics have received
much attention for distinguishing healthy and pathologic cardiac systems.
Despite structural peculiarities of the fetal cardiovascular system, the fetal
heart rate(FHR) displays multiple time scale characteristics similar to the
adult heart rate due to the autorhythmicity of its different oscillatory
tissues and its interaction with other neural controllers. In this paper, we
investigate the event and time scale characteristics of the normal and two
pathologic fetal heart rate groups with the help of the new measure, called the
Unit Time Block Entropy(UTBE), which approximates the entropy at each event and
time scale based on symbolic dynamics. This method enables us to match the
measurement time and the number of words between fetal heart rate data sets
simultaneously. We find that in the small event scale and the large time scale,
the normal fetus and the two pathologic fetus are completely distinguished. We
also find that in the large event scale and the small time scale, the presumed
distress fetus and the acidotic distress fetus are significantly distinguished.
