Ontogeny and control of the heart rate power spectrum in the last third of gestation in fetal sheep

•  What is the central question of this study? Can power spectral analysis of fetal heart rate variability provide a reliable, objective estimate of autonomic balance before birth? •  What is the main finding and its importance? This study demonstrates that there is a substantial increase in fetal heart rate spectral power over late gestation in chronically instrumented fetal sheep, with changes between sleep states that are consistent with known patterns of autonomic activity. However, parasympathetic blockade with atropine and complete chemical sympathectomy did not support substantial, consistent differences in the frequencies of sympathetic and parasympathetic activity in late gestation, suggesting that this does not provide a reliable index of relative cardiac autonomic activity before birth.

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