Intrapartum monitoring of high-risk deliveries with ST analysis of the fetal electrocardiogram: an observational study of 6010 deliveries

Objective: To evaluate the clinical use of ST analysis (STAN) for intrapartum monitoring of high-risk pregnancies.

Design: Prospective observational study.

Setting: University hospital, Norway, 2004-2008.

Population: Singleton pregnancies with a gestational age above 35(+6) weeks.

Methods: Analysis of maternal and neonatal outcomes for all deliveries according to the method of intrapartum monitoring.

Main outcome measures: Prevalence of cord metabolic acidosis (pH < 7.05, extracellular fluid base deficit (extracellular fluid) >12 mmol/L).

Results: Of 23 203 deliveries, 6010 (25.9%) were monitored with STAN. Fetal blood sampling was performed in 146 (2.4%) of the 6010 cases. During the study period, the prevalence of cord metabolic acidosis and moderate cord acidosis (pH < 7.15) decreased in STAN-monitored deliveries from 1.4 to 0.3% (p = 0.01) and from 16.4 to 11.7% (p = 0.001), respectively. The prevalence of moderate and severe neonatal encephalopathy was 0.38%. In the birth population, the proportion of cesarean deliveries decreased from 10.1 to 8.8%. The risk of emergency cesarean section after STAN monitoring compared with those monitored with auscultation/cardiotocography was high (odds ratio 5.4, 95% confidence interval = 4.9-6.1) but remained stable during the study period.

Conclusions: ST analysis is a useful tool for identification of fetuses at risk of intrapartum hypoxia. Despite the restricted use of fetal blood sampling, we found a low proportion of cord metabolic acidosis and newborn morbidity.