Objective: To relate the T/QRS ratio of the fetal electrocardiogram (ECG) to the cardiotocogram (CTG) and fetal pH during labour.
Design: Prospective data collection from selected monitored labours.
Setting: A postgraduate teaching hospital delivery suite.
Subjects: 113 women in labour at term.
Main outcome measures: Correlation of fetal T/QRS ratio values with pH values at the time of fetal blood sampling and at birth (umbilical artery blood). Comparison of the predictive values of raised T/QRS ratio and a pathological CTG for fetal acidemia.
Results: Complete data sufficient for analysis was available for 51 fetal scalp blood samples and 93 umbilical artery pH samples. The median (range) of T/QRS ratio values before birth of 88 babies not requiring admission to the neonatal unit was 0.13 (0.00-0.32) with a 97.5th centile value of 0.28. T/QRS ratios did not correlate with fetal scalp pH values. Fetal scalp acidaemia (pH less than 7.20) was detected with rates of 50 and 13% respectively by a pathological CTG and by a T/QRS ratio above 0.28, the positive predictive values being 40% and 50%, respectively. There was a significant correlation between increasing T/QRS ratio and falling pH. Detection rates (sensitivities) for umbilical artery acidaemia (pH less than 7.12) were 76% and 29% whereas positive predictive values were 38% and 71% respectively for a pathological CTG and a T/QRS ratio above 0.28.
Conclusion: A raised T/QRS ratio (greater than 0.28) had a considerably lower detection rate for fetal acidaemia during labour than a pathological CTG.