A portable phonocardiographic fetal heart rate monitor

In this paper we present a portable PDA-based fetal heart monitor that is able to provide instantaneous fetal heart rate (FHR) for the pregnant women. Several signal processing techniques are implemented in our device to make it clear, reliable and ease-to-use. Firstly the spectral subtraction method is used to remove the stationary background noise and the amplitude modulation technique is then employed to make the fetal heart sound more audible. A real time algorithm is proposed to extract the FHR information from the weak and noisy signals. Based on the signal spectrum distribution, a confidence factor (CF) is designed to forecast the reliability of the calculated FHR. CF can also be used to guide the user in locating the optimum auscultation position. Our device has been tested in a local hospital on a sample group of 41 pregnant women. It has been shown that an approximate 75% of the pregnant mothers are able to hear their babies' heart sound clearly by using our device. Tests are also carried out to compare our resulted FHR with the cardiotocography (CTG) records.