Review of the First 1502 Cases of ECG-ST Waveform Analysis During Labor in a Teaching Hospital

Abstract

Although electronic fetal monitoring has lowered the rate of intrapartum stillbirth, intrapartum asphyxia still is a major cause of long-term deficits in survivors. A recent Cochrane review found less metabolic acidosis, fewer operative deliveries, and a significant reduction in neonatal encephalopathy (NNE) when performing cardiotocography with ST waveform analysis (CTG-ST). This prospective observational study, carried out at a tertiary referral labor ward, evaluated the STAN™ monitoring system of ST-segment analysis in 1502 women who had a suspicious or abnormal CTG or a high-risk pregnancy. Monitoring entails the application of a fetal scalp electrode that provides continuous CTG and fetal ECG analysis. The ST waveform reflects what takes place during ventricular repolarization. STAN analysis deals with the ability of the fetal heart to adapt to hypoxia, as opposed to fetal blood sampling, which is done to detect acidosis. STAN analysis indicated the need for some action in 358 of the 1502 women in the trial-nearly one-fourth of those studied. In 2.4% of cases, traces could not be interpreted. Cord blood gas values were available in 836 cases, in 23 of which (2.8%) metabolic acidosis was documented. STAN monitoring identified 16 of these cases (70%). In all, 14 cases of NNE were monitored by STAN. A retrospective analysis showed the most frequent reasons for a poor outcome to be delay in taking action when an ST event and CTG called for delivery, and lack of intervention after 90 minutes of active second-stage labor with an abnormal CTG trace despite a normal ST trace. In the authors' experience, the use of ECG-ST waveform analysis to monitor high-risk labors has not altered the frequency of either NNE or emergency operative delivery. More intensive training in CTG and ST analysis appears to be needed, emphasizing the need for prompt action when significant CTG and ST-segment changes are present.