A novel portable instrument for long-term recording of fetal heart rate has been developed, based on the detection and evaluation of maternal abdominal acoustic signals. Multichannel, adaptive digital filtering using different frequency characteristics yields a reliable indication of fetal heart beats even at a high level of noise. The evaluation system statistically processes the acoustic signals, controls amplitude limits, and adjusts filter characteristics. Heart-rate variations of as much as 25/min/sec have been accurately registered. High-level integration enables the realization of the method in a very small, belt-mounted instrument with low power consumption, thus convenient for home use. The more than 40 hours of recorded detections stored in the built-in flash memory can be read back into a personal computer for medical inspection and analysis.
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