Biphasic ST should not be omitted from STAN clinical guidelines

Sir, We read with interest the study of Becker et al. on the added predictive value of biphasic events in ST analysis (STAN) (1). The authors used the cardiotocography (CTG) arm of the Swedish randomized controlled trial where STAN was recorded, but blinded for the clinician. Cases with Biphasic ST and concomitant CTG abnormalities indicating intervention were compared with all remaining cases without Biphasic ST. The authors concluded that the presence of significant biphasic events did not discriminate in the prediction of interventions for fetal distress or adverse outcome and therefore should be omitted from clinical guidelines if future studies confirm their findings. In our opinion the “added predictive value” investigated by the authors is clinically irrelevant. Biphasic ST is not an additional tool, but an integral part of the STAN clinical guidelines equal and parallel to baseline T/QRS changes (baseline or episodic T/QRS rise). The aim of fetal monitoring is to discriminate fetuses threatened by intrapartum hypoxia from those that are tolerating labor well. To test the predictive ability of Biphasic ST for intrapartum hypoxia the reference group should consist of fetuses that – according to the STAN clinical guidelines – did not have an indication for intervention for fetal distress. However, the control group in the study comprises deliveries: