Several studies have evaluated ST-segment changes with fetal monitoring. In one randomized trial of 2400 pregnancies, neonatal outcomes were not improved compared with those in which conventional fetal monitoring alone was used (Westgate, 1993). However, the cesarean delivery rate for fetal distress declined in those with ST-segment analysis. Amer-Wahlin and colleagues (2001, 2007) found that the addition ofST-segment analysis to conventional fetal monitoring significantly lowered cesarean delivery rates for fetal distress and reduced metabolic acidemia in umbilical artery blood.
A Normal ST• Aerobic metabolism B Generation ofT:QRS ratios• Positive energy balance raw-ECG Average of 30 ECG complexes IncreasedT-wave amplitude• Hypoxia/anaerobic metabolism• Adrenaline surge R T ratio
FIGURE 24-24 A. ST segment changes in normal and hypoxic conditions. B. Generation ofT:QRS ratios. (Redrawn with permission from Devoe L: ECG analysis: the next generation in electronic fetal monitoring? Contemporary Ob/Gyn, September 15,o2006.)
Subsequently, Doria and associates (2007) introduced STAN as a clinical practice and reported no changes in the incidence of operative delivery or neonatal encephalopathy. And, one metaanalysis of ive randomized trials comprising 15,352 patients found that ST-segment analysis did not lower rates of cesarean delivery or fetal metabolic acidemia at birth (Becker, 2012).
Last, in a trial by the NICHD, 5532 women were randomly assigned to an ST-segment analysis arm (the open group) and 5576 to standard intrapartum management (the masked group). he primary outcome was a composite of one or more of seven events associated with fetal compromise (Belfort, 2015). In the open group, clinical practice was directed to some degree by predetermined ST-segment analysis guidelines. hese stipulated that intervention should be withheld, that is, expectant management adopted, for at least 60 minutes despite the presence of minimal variability; variable decelerations lasting �60 seconds or dropping to �60 bpm; recurrent late decelerations; or prolonged decelerations lasting >2 minutes, so long as no ST-eventwas present. hese guidelines did not pertain to the standard usual management group. Notably, in the open group, 55 women were delivered when STAN guidelines indicated that labor should continue. his composed 20 percent ofthe total 287 cesarean deliveries performed for fetal distress in this group. Clearly, the attending physicians abandoned the open group protocol that stipulated nonintervention. They likely perceived the fetal heart rate patterns to reflect those formerly accepted in their usual practice as nonreassuring.
FIGURE 24-25 Biphasic ST-segment waveform with progressive fetal hypoxia. (Adapted with permission from Devoe L: ECG analysis: the next generation in electronic fetal monitoring? Contemporary Ob/Gyn, September 15,o2006.)
The results of this trial showed that STAN had no efect on neonatal outcome or cesarean delivery rates (Belfort, 2015). In their review, Neilson and colleagues (2015) reached similar conclusions. hese results have essentially eliminated use ofSTsegment analysis in the United States, but this technology is still used in Europe.
Doppler interrogation of the umbilical artery has been studied as another potential adjunct to conventional fetal monitoring. Further described in Chapter 10 (p. 213), abnormal Doppler waveforms may signiy pathological umbilical-placental vessel resistance. From their review, Farrell and associates (1999) concluded that this technique, used intrapartum, was a poor predictor of adverse perinatal outcomes.