BACKGROUND AND PURPOSE:

• Electronic fetal monitoring (EFM) is commonly used in the US, although data is lacking that there is benefit and may have contributed to increased cesarean section rates
• Using modern definitions, Cahill et al. (AJOG, 2018) assessed which EFM patterns predict acidemia

METHODS:

• Prospective cohort study
• Participants: Women laboring at ≥37 weeks’ gestation with a singleton cephalic fetus
• EFM patterns during the last 120 minutes prior to delivery were analyzed
• NICHD category system criteria were used as well as novel patterns
• Estimated deceleration area: Sum of the areas within the deceleration
  • Each area was estimated as ½ × duration × depth
• Primary outcome: Fetal acidemia (umbilical artery pH ≤7.10)
• Secondary outcomes:
  • Neonatal composite morbidity, which included any ≥1 of the following
    • Mechanical ventilation | Seizures | Sepsis | RDS | meconium aspiration | Hypothermia | Death
  • Area under the receiver operating characteristic curves (AUC) were used to assess the test characteristics of individual models for acidemia and neonatal morbidity
  • DeLong method, rather than overlapping confidence intervals were used to compare AUCs
  • Youden index was used to identify the optimal cut points of total deceleration for acidemia or neonatal morbidity to maximizes the sum of sensitivity and specificity

RESULTS:

• 8,580 women were included in the study
  • 1.7% delivered acidemic infants
  • Composite neonatal morbidity was diagnosed in 8.8% neonates
• Persistent category I (although rare) was associated with normal pH
  • Mostly category 1 or ever category 1 were more likely to have a normal pH
• Moderate variability alone (always, mostly, ever) did not independently predict normal pH
• Any acceleration during 120 minutes whether spontaneous or induced with scalp stimulation was associated with normal pH
  • Adjusted risk ratio of 1.02; 95% CI, 1.01–1.03
• Ever category III, while rare, was associated with acidemia (there were no all or mostly time periods)
  • Adjusted risk ratio of 8.72, 95% CI, 2.92-26.04
• Total deceleration area was most discriminative of acidemia
  • AUC 0.76; 95% CI, 0.72-0.80
• Deceleration area with any 10 minutes of tachycardia was most discriminative for neonatal morbidity
  • AUC 0.77; 95% CI, 0.75-0.79)
• Threshold of deceleration area
  • Prediction of acidemia: 42,152
  • Prediction of newborn morbidity: 50,761
• Number of cesareans needed-to-be performed once the above thresholds are reached
  • To potentially prevent 1 case of acidemia and morbidity requires 5 and 6 cesarean sections, respectively

CONCLUSION:

• Persistent category I was significantly associated with normal pH and any 10 minute period of category III was associated with acidemia
• Deceleration area is the most predictive electronic fetal monitoring pattern for acidemia; deceleration and tachycardia for neonatal morbidity
• The authors state

While EFM remains a poor screening test, clinically, these patterns can help identify infants developing acidemia. At identifiable thresholds of deceleration area, the NNT of cesareans to potentially prevent 1 case of acidemia or morbidity was relatively low. These specific features of EFM patterns should be considered in the clinical interpretation and algorithms to improve the performance of EFM

Learn More – Primary Sources:

A prospective cohort study of fetal heart rate monitoring: deceleration area is predictive of fetal acidemia.

Related ObG Topics:

Category II Tracings, Algorithms and Recognition of Metabolic Acidemia

Electronic Fetal Monitoring vs. Intermittent Auscultation