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. Bland-Altman 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.