Fetal heart rate recorder for long-duration use in active full-term pregnant women.

We sought to assess the signal consistency and accuracy of a long-duration fetal heart rate (FHR) recorder (a 1-MHz ultrasonic Doppler transducer composed of six miniprobes and an autocorrelation technique) in active, full-term pregnant women. The FHR data of 15 normal full-term fetuses were obtained every 250 milliseconds in various maternal positions using the new Doppler system or a direct scalp electrocardiographic (ECG) transducer. Differences between simultaneous Doppler and ECG measures were small and within acceptable limits except for short-term variability. Signal loss, assessed in 15 subjects in various positions, was less than 10% except during sitting or walking. The mean (+/- standard deviation) percentages of FHR signals lost over 2 hours in bed, 1 hour out of bed, and 24 hours in and out of bed were 1.2 +/- 2.1, 12.9 +/- 16.2, and 3.8 +/- 4.4, respectively. This system for recording FHR is suitable for clinical research and routine FHR monitoring, and provides data comparable to Holter ECG monitoring in patients with heart disease.