Cardiotocography only versus cardiotocography plus ST analysis of fetal electrocardiogram for intrapartum fetal monitoring: a Swedish randomised controlled trial

Background Previous studies indicate that analysis of the ST waveform of th e fetal electrocardiogram provides information on the fetal response to hyp oxia. We did a multicentre randomised controlled trial to test the hypothes is that intrapartum monitoring with cardiotocography combined with automati c ST-waveform analysis results in an improved perinatal outcome compared wi th cardiotocography alone. Methods At three Swedish labour wards, 4966 women with term fetuses in the cephalic presentation entered the trial during labour after a clinical deci sion had been made to apply a fetal scalp electrode for internal cardiotoco graphy. They were randomly assigned monitoring with cardiotocography plus S T analysis (CTG+ST group) or cardiotocography only (CTG group). The main ou tcome measure was rate of umbilical-artery metabolic acidosis (pH <7.05 and base deficit >12 mmol/L). Secondary outcomes included operative delivery f or fetal distress. Results were first analysed according to intention to tr eat, and secondly after exclusion of cases with severe malformations or wit h inadequate monitoring. Findings The CTG+ST group showed significantly lower rates of umbilical-art ery metabolic acidosis than the cardiotocography group (15 of 2159 [0.7%] v s 31 of 2079 [2%], relative risk 0.47 [95% CI 0.25-0.86], p=0.02) and of op erative delivery for fetal distress (193 of 2519 [8%] vs 227 of 2447 [9%], 0.83 [0.69-0.99], p=0.047) when all cases were included according to intent ion to treat. The differences were more pronounced after exclusion of 291 i n the CTG+ST group and 283 in the CTG group with malformations or inadequat e recording. Interpretation Intrapartum monitoring with cardiotocography combined with a utomatic ST-waveform analysis increases the ability of obstetricians to ide ntify fetal hypoxia and to intervene more appropriately, resulting in an im proved perinatal outcome.