. 2020 Mar 16;6(1):e000658. doi: 10.1136/bmjsem-2019-000658

Table 4.

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 GA^{115 116} (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 GA^{42 118}	An increase is associated with vagal and sympathetic activity which may be associated with the ability to respond to regulatory mechanisms^{48 119 120}
	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.