  The overarching goal of the present work is to contribute to the
understanding of the relations between fetal heart rate (FHR) temporal dynamics
and the well-being of the fetus, notably in terms of predicting cardiovascular
decompensation (CVD). It makes uses of an established animal model of human
labor, where fourteen near-term ovine fetuses subjected to umbilical cord
occlusions (UCO) were instrumented to permit regular intermittent measurements
of metabolites, pH, and continuous recording of electrocardiogram (ECG) and
systemic arterial blood pressure (to identify CVD) during UCO. ECG-derived FHR
was digitized at the sampling rate of 1000 Hz and resampled to 4Hz, as used in
clinical routine. We focused on four FHR variability features which are tunable
to temporal scales of FHR dynamics, robustly computable from FHR sampled at
$4$Hz and within short-time sliding windows, hence permitting a time-dependent,
or local, analysis of FHR which helps dealing with signal noise. Results show
the sensitivity of the proposed features for early detection of CVD,
correlation to metabolites and pH, useful for early acidosis detection and the
importance of coarse time scales (2.5 to 8 seconds) which are not disturbed by
the low FHR sampling rate. Further, we introduce the performance of an
individualized self-referencing metric of the distance to healthy state, based
on a combination of the four features. We demonstrate that this novel metric,
applied to clinically available FHR temporal dynamics alone, accurately
predicts the time occurrence of CVD which heralds a clinically significant
degradation of the fetal health reserve to tolerate the trial of labor.
