FIG 6.23 Sample report on a fetal electrocardiogram from a singleton pregnancy at 35 weeks’ gestation (From Taylor MJ, Smith MJ, Thomas M, et al Non-invasive fetal electrocardiography in singleton and multiple pregnancies Br J Obstet Gynaecol 2003;110:668-678.) FIG 6.24 Representative averaged magnetoelectrocardiographic waveforms recorded during fetal life (A) Normal fetus at 39 weeks’ gestation (B) Normal fetus at 37 weeks’ gestation (C) Fetus at 27 weeks’ gestation but with ventricular tachycardia at 25 weeks’ gestation (D) Fetus at 27 weeks’ gestation with supraventricular tachycardia (E) Fetus with supraventricular tachycardia at 31 weeks’ gestation (F) Same fetus as in (C) but with tachycardia present at 25 weeks’ gestation (G–H) Fetuses with complete atrioventricular block at 30 and 25 weeks’ gestation, respectively (I) Fetus with blocked premature atrial contractions at 20 weeks’ gestation All waveforms are taken from the channel with the largest signal amplitude, the amplitude being shown in units of ferntotesla, with each ferntotesla equal to 10−15 Tesla (From Zhao H, Strasburger JF, Cuneo BF, Wakai RT Fetal cardiac repolarization abnormalities Am J Cardiol 2006;98:491–496.) Heart rate variability may also be described using the standard deviation from the time domain, as well as other measures from the frequency domains and approximate entropy as a measure of complexity.213 Two distinct fractal structures have been identified within this variation They show significant gestational change in the normal fetus and may be useful to evaluate variation in disease states.214 Investigation into variability of the heart rate in the fetus and neonate may provide insights into developmental processes in health and disease and refine stratification of fetuses at risk of intrauterine death, as well as the risk of sudden infant death syndrome in those born prior to term Neonates who have suffered apparent life-threatening events show differences in heart rate variability, suggesting altered autonomic control.215,216 Fetal heart rate parameters such as average acceleration and deceleration capacity may prove more useful in the detection of the small for dates fetus, thus improving prenatal detection of poor fetal growth and improving outcomes.217