Method and apparatus for measuring fetal heart rate and an electroacoustic sensor for receiving fetal heart sounds

Method and apparatus for long-term, non-invasive measuring of fetal heart rate. The method utilizes the characteristic curves of first and second heart sound received by the preferred electroacoustical converter. The identification and distinction of first and second sounds, furthermore their time relation used for heartbeat identification highly increase the reliability of fetal heart rate determination. The distinction of first and second sound is based on the differences in frequency spectrums measured in a relatively short time window and by the estimation of the power peaks measured on two test frequencies chosen on the two ends of the frequency range of fetal heart sound. The method is implemented in an integrated apparatus to achieve low power consumption for battery-operated long-term measurements. Digital filtering and selective power estimation is applied for continuous computation of power time function on the two test frequencies. The test frequencies can be adaptively modified depending on individual fetal parameters to improve the distinction of the first and second sound. The apparatus is capable to registrate, store and transfer data of fetal heart rate and womb contractions to a personal computer.