Separation of fetal and maternal ECG complexes from a mixed signal using an algorithm based on linear regression.

Fetal scalp ECG and Doppler ultrasound are the two methods universally used to derive the fetal heart rate (FHR) for cardiotocography. Other fetal signal sources have not been used successfully because of the complexity of the signal and the need for an additional maternal ECG input. In this paper, we present an algorithm for separating the fetal and maternal ECG signals obtained from intrauterine electrodes during labour. The algorithm detects all occurrences of ECG complexes and uses linear regression functions to compare each complex with a set templates. Sets of templates are identified as either maternal or fetal in origin and two signals are output for heart rate measurement. The outputs are also processed to eliminate artefacts that may occur when the maternal and fetal complexes are coincident. The algorithm processes 10 seconds of data at a time (in about 200 ms on a standard PC) while a further 10 s of data is being acquired. It has the advantage that no extra input is required, such as maternal ECG obtained from chest leads, and only assumes that two different populations of complexes of two different shapes are present in the input signal. The algorithm could also be used for the separation of fetal and maternal signals obtained from abdominal electrodes.