Comprehensive and Detailed Explanation From Exact Extract–Based NCC C-EFM References:
Variability reflects the interplay of the autonomic nervous system—sympathetic and parasympathetic influences—on the fetal myocardium. NCC defines variability as variation in the R–R intervals on the fetal ECG.
Key points:
Variability originates from beat-to-beat fluctuations in ventricular depolarization timing.
These R–R interval changes result from baroreceptor and chemoreceptor responses, vagal modulation, and fetal behavioral states.
Carbon dioxide levels affect chemoreceptors but do not directly define variability.
Thus, variability is best described as resulting from variance in R–R intervals.
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