Improved Doppler ultrasonic monitoring of the foetal heart rate

Abstract

The Doppler ultrasonic technique for the monitoring of the foetus has been available for well over a decade. It offers a noninvasive assessment of the condition of the foetus and has therefore become an important antenatal technique. However, the foetal heart rate information obtained by this technique is considered to be less precise than that obtained from the foetal e.c.g. The waveforms recorded by the Doppler ultrasonic method are complex and variable and this often leads to difficulty in identifying a reliable and regular measuring point within these waveforms from which to calculate the heart rate. This has resulted in a cautious acceptance of ultrasonically determined foetal heart-rate records. This paper does not dispute the difficulties of interpreting such rate information, but outlines a pair of algorithms for processing and presenting a more accurate and reliable indication of the foetal heart rate determined from the Doppler ultrasonic method. These algorithms calculate a two second average rate from only those intervals which have been determined to be ‘valid’, based on the criterion that they should be within ±10% of the most previous valid interval.