BACKGROUND Animal and human studies have shown that fetal hypoxaemia during labour can alter the shape of the fetal electrocardiogram (ECG) waveform, notably (1) the relation of the PR to RR intervals and (2) elevation or depression of the ST segment. Technical systems have therefore been developed to monitor the fetal ECG during labour as an adjunct to continuous electronic fetal heart rate monitoring with the aim of improving fetal outcome and minimising unnecessary obstetric interference. OBJECTIVE To compare the effects of analysis of fetal ECG waveforms during labour with alternative methods of fetal monitoring. METHODS The Cochrane Pregnancy and Childbirth Group trials register was searched (September 2002). METHODS Randomised trials comparing fetal ECG waveform analysis with alternative methods of fetal monitoring during labour. METHODS Trial quality assessment and data extraction were performed by the reviewer, without blinding. RESULTS Three trials including a total of 8357 pregnant women were included. The trials were of sound methodological quality. All three trials assessed the use of the fetal ECG as an adjunct to continuous electronic fetal heart rate monitoring during labour. One study assessed PR intervals; two assessed the ST segment. The use of ST waveform analysis (7400 women) was associated with fewer babies with severe metabolic acidosis at birth (cord pH less than 7.05 and base deficit greater than 12 mmol/L) (relative risk (RR) 0.44, 95% confidence interval (CI) 0.26 to 0.75, data from 6672 babies). This was achieved along with fewer fetal scalp samples during labour (RR 0.86, 95% CI 0.76 to 0.98) and fewer operative deliveries (RR 0.89, 95% CI 0.82 to 0.97). Apart from a trend (that did not achieve statistical significance) towards fewer operative deliveries (RR 0.87, 95% CI 0.76 to 1.01), there was little evidence that monitoring by PR interval analysis conveyed any benefit. This may reflect limitations of the technique or, alternatively, the smaller numbers available for analysis from the single trial (957 women). CONCLUSIONS These findings support the use of fetal ST waveform analysis when a decision has been made to undertake continuous electronic fetal heart rate monitoring during labour. However, in most labours, technically satisfactory cardiotocographic traces can be obtained by external ultrasound monitors which are less invasive than internal scalp electrodes (which are required for electrocardiographic (ECG) analysis). A better approach might be to restrict fetal ST waveform analysis to those fetuses demonstrating disquieting features on cardiotocography.