Fetal ECG waveform analysis should improve fetal surveillance in labour.

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Abstract
Fetal heart rate (FHR) and fetal electrocardiogram (ECG) recordings were obtained from a scalp electrode with maternal thigh as reference and used for ST waveform analysis in 201 patients in labour. Nearly 45% had suspicious or abnormal FHR traces whilst only 27% had T/QRS ratio > 0.25 (mean .+-. 2 SD). A normal T/QRS ratio identified 99.3% of fetuses with normal buffering capacity in cord artery blood. Of 13 infants with a cord artery blood pH < 7.15, standard bicarbonate was < 15.0 mmol/l in five who had an average T/QRS ratio < 0.25 throughout labour. Of the eight with respiratory acidosis, five had an increase in T/QRS ratio > 0.25 for longer than 20 minutes prior to delivery, in two the ration increased during the last few minutes and one had no change (pH 7.14). Persistent elevation of T/QRS in the first stage of labour identified those with decrease in buffer capacity in cord arterial blood (sensitivity of 94.1%). Acute hypoxia was recognized by the rapid rise in T/QRS. The specificity of T/QRS to identify fetuses at risk increased by combining the ST waveform analysis with FHR changes.

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