Supplementary Material for: Potential of Fetal Electrocardiography Monitoring in Evaluating Treatment Indications for Fetal Supraventricular Tachycardia

Introduction: Accurate assessment of fetal supraventricular tachycardia (SVT) frequency is critical for deciding treatment strategies. In this study, we evaluated the potential of prolonged non-invasive fetal electrocardiography (fECG) monitoring for assessing SVT and guiding therapy.
Case Presentation: A 37-year-old woman at 28 weeks of gestation was referred to our hospital for fetal tachycardia. The patient was diagnosed with fetal arrhythmia, including occasional premature atrial contractions and SVT. Fetal heart rate monitoring using Doppler-based cardiotocography (CTG) with external transducers was insufficient for accurate frequency evaluation; moreover, brief fetal echocardiography was inadequate due to marked diurnal variation in SVT frequency. Prolonged fECG monitoring at 29 and 31 weeks of gestation revealed that SVT did not persist for 12 or more hours or for more than 50% of the monitoring period, indicating a low risk for fetal hydrops. The pregnancy proceeded normally, and the infant was born healthy at 38 weeks.
Conclusion: This report suggests that prolonged fECG monitoring is a more reliable and less invasive method for assessing fetal SVT frequency compared with traditional CTG or fetal echocardiography. Furthermore, it provides a non-invasive and accurate approach for evaluating the need for fetal therapy, especially in arrhythmia cases where frequency assessment is essential.