Accuracy and reliability of fetal heart rate monitoring using maternal abdominal surface electrodes

Objective. Compare the accuracy and reliability of fetal heart rate identification from maternal abdominal fetal electrocardiogram signals (ECG) and Doppler ultrasound with a fetal scalp electrode. Design. Prospective open method equivalence study. Setting. Three urban teaching hospitals in the Northeast United States. Sample. 75 women with normal pregnancies in labor at >37 weeks of gestation. Methods. Three fetal heart rate detection methods were used simultaneously in 75 parturients. The fetal scalp electrode was the standard against which abdominal fetal ECG and ultrasound were judged. Main outcome measures. The positive percent agreement with the fetal scalp electrode indicated reliability. BlandAltman analysis determined accuracy. The confusion rate indicated how frequently the devices tracked the maternal heart rate. Results. Positive percent agreement was 81.7 and 73% for the abdominal fetal ECG and ultrasound, respectively (p = 0.002). The abdominal fetal ECG had a lower root mean square error than ultrasound (5.2 vs. 10.6 bpm, p < 0.001). The confusion rate for ultrasound was 20-fold higher than for abdominal ECG (8.9 vs. 0.4%, respectively, p < 0.001). Conclusion. Compared with the fetal scalp electrode, fetal heart rate detection using abdominal fetal ECG was more reliable and accurate than ultrasound, and abdominal fetal ECG was less likely than ultrasound to display the maternal heart rate in place of the fetal heart rate.