A Cochrane review [Abstract] 1 included 7 studies with a total of 27 403 women (6 studies were based on ST analysis and 1 on PR length). In comparison to continuous electronic fetal heart rate monitoring alone, the use of adjunctive ST waveform analysis made no significant difference to primary outcomes: births by caesarean section (RR 1.02, 95% CI 0.96 to 1.08; 6 trials, n=26 446), the number of babies with severe metabolic acidosis at birth (cord arterial pH less than 7.05 and base deficit greater than 12 mmol/L) (RR 0.72, 95% CI 0.43 to 1.20; 6 trials, n=25 682), or babies with neonatal encephalopathy (RR 0.61, 95% CI 0.30 to 1.22; 6 trials, n=26 410). There were, however, on average fewer fetal scalp samples taken during labour (RR 0.61, 95% CI 0.41 to 0.91; 4 trials, n=9671) although the findings were heterogeneous; there were fewer operative vaginal deliveries (RR 00.92, 95% CI 0.86 to 0.99; 6 trials, n=26 446) and admissions to special care unit (RR 0.96, 95% CI 0.89 to 1.04; 6 trials, n=26 410). There was little evidence that monitoring by PR interval analysis conveyed any benefit.
In a prospective cohort study 2 women in labor with a singleton fetus in cephalic position beyond 36 weeks of gestation were monitored with STAN and CTG. The relationship between "baseline T/QRS rise" and neonatal cord arterial acidemia and hypoxic distress were assessed using a linear mixed-model analysis. Baseline T/QRS rise" was not associated with neonatal acidemia in the presence of normal CTG, regardless of the magnitude of the T/QRS rise. However, in a linear mixed-model analysis, cord blood sodium levels were negatively (p = .033) associated with T/QRS ratio magnitude.
Comment: The quality of evidence is downgraded by study limitations (unclear blinding of outcome assessment) and by inconsistency (variability in results across studies).
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