The normal condition of the fetal electrocardiogram during labour

A real-time computer system was employed to monitor continuously the fetal electrocardiogram (ECG) during labour. Signals from a scalp electrode were amplified, filtered and passed through an interface system to a digital computer. From 110 patients studied, 37 were selected by rigid criteria which fulfilled a strict definition of normal fetal condition in labour and delivery. The mean values and the range of the various parameters of the fetal ECG complex were defined. As a large amount of data was generated by the system, a method was developed to display the short and long-term dynamic behaviour of the fetal ECG during labour in the form of labour profiles. By further averaging of these labour profiles, the pattern of normal behaviour was established. Certain changes in the fetal ECG, previously thought to be characteristic of fetal distress, occurred in normal patients. The P-R interval was up to 10 per cent shorter during contractions towards the end of labour and there was a long-term trend towards the end of labour for the P-R interval to fall by 7 per cent. The P wave amplitude fell by 30 per cent over the last hour. These trends were statistically significant. The QRS complex was found to lengthen slightly towards the end of labour, but the R-T interval and ST segment displacement displayed no significant changes.