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We present a passive acoustic apparatus for maternal abdominal fetal heart rate (FHR) monitoring. The apparatus consists of an acoustic sensor module and a Laptop or a PDA embedded with signal processing algorithms. It is able to provide a calculated fetal heart rate instantaneously, real-time fetal heart sound waveform displays and audio playback. The fetal heart sound signals are detected, de-noised and reconstructed by utilizing wavelet transform based signal processing approach. The proposed approach improves the signal to noise ratio which allows reliable fetal heart rate variation to be estimated under very weak signal environment. The apparatus has gone through clinical trials in a local hospital on a sample group of 41 pregnant women.