Improvements in the registration and analysis of fetal heart rate records at the bedside.

A microprocessor system is described for on-line analysis of the fetal heart rate detected by conventional Doppler systems. A brief account is given of the instrumentation and program structure. The system has been tested by analysing normal and abnormal antenatal fetal heart rate records. Pulse Doppler with autocorrelation measurement of the fetal pulse interval reduced the signal loss in clinical practice by a factor of 10, to an average of 2.1% in 629 records from uncomplicated pregnancies. Yet it is still necessary to identify signal loss, because it occasionally rises to unacceptable levels in association with fetal movements or hiccups. Medium-term measures of fetal heart rate variation (within 16-0.1 cycles/min) varied with gestational age, but were a better index of fetal well-being than longer-term measures. The application of the system to fetal monitoring is illustrated.