1. A passive fetal heart rate monitoring apparatus comprising: a passive fetal heart rate monitoring sensor having a plurality of sensor elements for acquiring acoustic signals emitted from a fetus inside a body and outputting a plurality of sensor signals in response to the acoustic signals; a signal processing device, including receivers, amplifiers, and filters for outputting a plurality of processed signals in response to the sensor signals; means for detecting fetal heart beats comprising a neural network, responsive to the plurality of processed signals, for identifying regions of fetal heart beats on each signal, and for outputting a functional value indicative of the presence of fetal heart beats for each processed signal; fetal heart rate determining means, responsive to the plurality of functional values indicative of the presence of fetal heart beats, for determining and outputting a fetal heart rate.