A processing device (100, 100') for determining a fetal heart rate from an ultrasonic Doppler echo signal, comprising: a reference demodulation unit (101, 101') arranged to demodulate the echo signal using a carrier frequency of the ultrasonic signal used for generating the echo signal as a demodulation frequency, thus providing a reference demodulated signal, a phase shift demodulation unit (102, 102') arranged to demodulate the echo signal using the demodulation frequency shifted by 90 degrees in comparison to the reference demodulation unit, thus providing a phase shift demodulated signal, a comparison unit arranged to compare the reference demodulated signal and the phase shift demodulated signal by comparing zero crossings and/or points of maximum positive and/or negative amplitude of the reference demodulated signal and the phase shift demodulated signal so as to obtain a binary sign signal including information on whether the phase shift demodulated signal leads or lags the reference demodulated signal, and a processing unit arranged to process the binary sign signal so as to determine timing information indicative of first portions of the echo signal corresponding to a movement in a first direction and of second portions of the echo signal corresponding to a movement in a second direction opposite to the first direction, wherein the processing unit is arranged to selectively cut out portions of a demodulated signal obtained by demodulating the echo signal based on the timing information, so to obtain a cut out demodulated signal, and wherein the processing unit is further arranged to determine the fetal heart rate using the cut out demodulated signal by means of autocorrelation. a reference demodulation unit (101, 101') arranged to demodulate the echo signal using a carrier frequency of the ultrasonic signal used for generating the echo signal as a demodulation frequency, thus providing a reference demodulated signal, a phase shift demodulation unit (102, 102') arranged to demodulate the echo signal using the demodulation frequency shifted by 90 degrees in comparison to the reference demodulation unit, thus providing a phase shift demodulated signal, a comparison unit arranged to compare the reference demodulated signal and the phase shift demodulated signal by comparing zero crossings and/or points of maximum positive and/or negative amplitude of the reference demodulated signal and the phase shift demodulated signal so as to obtain a binary sign signal including information on whether the phase shift demodulated signal leads or lags the reference demodulated signal, and a processing unit arranged to process the binary sign signal so as to determine timing information indicative of first portions of the echo signal corresponding to a movement in a first direction and of second portions of the echo signal corresponding to a movement in a second direction opposite to the first direction, wherein the processing unit is arranged to selectively cut out portions of a demodulated signal obtained by demodulating the echo signal based on the timing information, so to obtain a cut out demodulated signal, and wherein the processing unit is further arranged to determine the fetal heart rate using the cut out demodulated signal by means of autocorrelation.