Overview of parameters associated with fetal ANS
| Methods | Parameters | Description | Associated autonomic function | Over the course of pregnancy | Interpretation |
| Doppler ultrasound, CTG, dMMG (marker), fMCG, BPP | fHR | Fetal heart rate | Sympathetic and parasympathetic activity | Decreases slightly over GA115 116 (normal range: 110–150 beats/min)117 | Pathological fHR:<100 beats/min or >170 beats/min with a bandwidth of <5 and ≥90 min → indicates an insufficient fetal oxygen supply |
| fHRV | Fetal heart rate variability | Sympathetic and parasympathetic activity (sympatho-vagal balance) | Increases with GA42 118 | An increase is associated with vagal and sympathetic activity which may be associated with the ability to respond to regulatory mechanisms48 119 120 | |
| Fetal bradycardia and tachycardia | Fetal bradycardia: fHR <110 beats/min121 Fetal tachycardia: fHR >180 beats/min, present for more than at least 50% of the examination time122 | Irregularities in fHR rhythm | Fetal arrhythmias are detected in at least 2% of unselected pregnancies during the routine obstetrical ultrasound122 | Occurrence >10 min increases the risk of preterm delivery and higher perinatal morbidity and mortality.122 Transient sinus bradycardia:<2 min have no clinical implication123 | |
| Doppler ultrasound, CTG, dMMG (marker), fMCG, BPP | Fetal body movements | Can be indirectly detected through fMCG beginning at 18 GA41 | fHR | Increases over the course of pregnancy 124 | A reduction in fetal movements is associated with adverse pregnancy outcomes in pregnancy124 |
ANS, autonomic nervous system; BPP, biophysical profile; CTG, cardiotocography; dMMG, diaphragmatic magnetomyogram ; fHR, fetal heart rate; fHRV, fetal heart rate variability; fMCG, fetal magnetocardiography; GA, gestational age; HRV, heart rate variability.