ECG waveform analysis in intrapartum fetal monitoring.

Intrapartum cardiotocography (CTG) has a high false positive rate and, in the absence of facilities for fetal scalp blood sampling, is associated with increased operative deliveries for 'fetal distress'. It is presently possible to obtain a representative fetal ECG signal using the fetal scalp electrode. There is renewed interest in fetal ECG waveform analysis in the hope that it will improve the specificity of detecting intrapartum fetal hypoxia when there is an abnormal fetal heart rate pattern. Two portions of the fetal ECG are potentially useful: the ST waveform (T/QRS ratio) and the PR interval correlated with the RR interval. Animal experiments suggest that changes in the ST waveform, increase in the T wave amplitude in particular, reflect myocardial anaerobic metabolism. Clinical studies have shown poor correlation between the T wave changes and fetal heart rate changes. There is also concern that the sensitivity of the ST waveform changes for fetal acidaemia may be poor. More information is required before its use is incorporated into routine clinical practice.