FOETAL ELECTROCARDIOGRAPH

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References: 9

The ECG signal from the foetal heart can be detected on the abdomen of the mother, or directly from an electrode on the scalp of the foetus, as soon as this is exposed through the cervix during the first stage of labour. The heart rate information so derived is used during labour to monitor the state of the foetus, since the fluctuations in rate which occur as a result of uterine contractions provide an important indicator of foetal wellbeing. Scalp electrodes are used and these may be small suction cups with a spike electrode at the centre, small metal 'crocodile' jaws squeezed together with a special tool on to the foetal scalp, or a sharp wire screw which is rotated to pass into the skin of the scalp.

If the ECG is detected through the abdominal wall of the mother then the signal is very small and is subject to interference from the ECG of the mother. Electronic processing may enable a separation of the two so that foetal heart rate can be monitored at earlier stages of pregnancy. It is more common now to use doppler ultrasound foetal heart detectors in both of these applications until the foetal scalp is well exposed during labour when the scalp electrode is the preferred method of monitoring the rate.

The foetal electrocardiograph is normally incorporated into an instrument which also monitors the uterine contractions, and the whole instrument is called a cardiotocograph or a foetal heart monitor.