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Sympathetic neural activation does not mediate heart rate variability during repeated brief umbilical cord occlusions in near‐term fetal sheep

Fetal heart rate variability and changes in the ST segment of the electrocardiogram are used clinically during labour to identify fetuses at risk of severe metabolic acidosis or death. Sympathetic nervous system activity contributes to heart rate variability in healthy normoxic fetuses, and is critical for the rapid haemodynamic adaptations to repeated episodes of asphyxia induced by brief complete umbilical cord occlusions at rates consistent with active labour. We now show that chemical sympathectomy did not alter fetal heart rate variability between episodes of brief repeated asphyxia or elevation of the ST segment during asphyxia. The lack of influence of the sympathetic system on fetal heart rate variability between episodes of brief asphyxia suggests that measures of fetal heart rate variability are unlikely to help monitor changes in sympathetic nervous system activity during active labour.