What is electronic fetal heart monitoring?

Electronic Fetal Heart Monitoring

Electronic fetal heart monitoring (EFM) is a widely used technology for assessing fetal well-being during labor that can reduce neonatal seizures but has not been shown to decrease cerebral palsy or neonatal mortality rates while increasing cesarean and instrumental delivery rates. 1

Definition and Purpose

Electronic fetal monitoring is a technology developed in the 1960s to assist in the diagnosis of fetal hypoxia during labor. It involves continuous recording of the fetal heart rate (FHR) and uterine contractions using external or internal transducers. By 2002, approximately 85% of live births in the United States were monitored using EFM 1.

The primary purpose of EFM is to detect signs of fetal distress that might indicate:

• Hypoxic-ischemic encephalopathy
• Cerebral palsy
• Impending fetal death

Types of Fetal Monitoring

Continuous Electronic Fetal Monitoring

• Uses external transducers or internal electrodes to continuously record FHR and uterine contractions
• External monitoring: Uses Doppler ultrasound technology fixed to maternal abdomen
• Internal monitoring: Uses electrodes attached to fetal scalp (requires ruptured membranes)

Structured Intermittent Auscultation

• Systematic use of Doppler assessment of FHR at defined intervals
• Equivalent to continuous EFM for low-risk pregnancies
• Requires 1:1 nurse-to-patient ratio
• Protocol typically includes:
  • Every 15-30 minutes during first stage of labor
  • Every 5 minutes during second stage of labor
  • Assessment before and after procedures, medication administration, etc. 1

Interpretation of EFM Tracings

The National Institute of Child Health and Human Development established standardized terminology for interpreting EFM tracings. The DR C BRAVADO mnemonic provides a systematic approach 1:

• Determine Risk: Assess maternal and fetal risk factors
• Contractions: Evaluate rate, rhythm, frequency, duration, intensity
• Baseline Rate: Normal (110-160 bpm), bradycardia (<110 bpm), tachycardia (>160 bpm)
• Variability: Absent, minimal, moderate, or marked
• Accelerations: Presence indicates fetal well-being
• Decelerations: Early, variable, late, or prolonged
• Overall assessment: Categorization and management plan

FHR Categories

EFM tracings are classified into three categories 1, 2:

1. Category I (Normal):

   • Normal baseline rate (110-160 bpm)
   • Moderate variability
   • No late or variable decelerations
   • May have accelerations
   • No intervention required

2. Category II (Indeterminate):

   • All tracings not categorized as I or III
   • Requires close monitoring and may need intervention
   • Presence of moderate variability and accelerations with absence of recurrent pathologic decelerations provides reassurance

3. Category III (Abnormal):

   • Absent variability with recurrent late decelerations, recurrent variable decelerations, or bradycardia
   • Sinusoidal pattern
   • Requires immediate intervention and expedited delivery if pattern doesn't improve

Clinical Efficacy and Limitations

The evidence regarding continuous EFM shows mixed results:

• Benefits:

  • Reduces neonatal seizures (NNT = 661) 1, 3
  • May detect early signs of uterine rupture in trial of labor after cesarean 3

• Limitations:

  • No reduction in cerebral palsy rates 1, 3
  • No reduction in overall neonatal mortality 1, 3
  • Increases cesarean delivery rates (NNH = 20) 1, 3
  • Increases instrumental vaginal births (NNH = 33) 1, 3
  • High false-positive rate (99%) due to low prevalence of adverse events 2

Management of Abnormal Tracings

When abnormal patterns are detected, intrauterine resuscitation measures include 3, 2:

• Changing maternal position
• Discontinuing oxytocin if being used
• Administering oxygen
• Performing vaginal examination
• Administering IV fluids
• Considering amnioinfusion for variable decelerations

If these measures don't improve Category III tracings, expedited delivery should be considered 2.

Technological Advances

Recent developments in EFM technology include:

• Deep learning algorithms for automated interpretation 4
• Integration with other monitoring modalities
• Improved signal processing techniques for better accuracy 5

Common Pitfalls in EFM Interpretation

• Overreliance on EFM without considering clinical context
• Failure to recognize normal variations (e.g., sleep cycles causing decreased variability)
• Misinterpretation of patterns leading to unnecessary interventions
• Interobserver variability in interpretation
• Using admission EFM tracings for low-risk pregnancies, which increases interventions without improving outcomes 1

Choosing the Appropriate Monitoring Method

• Low-risk pregnancies: Structured intermittent auscultation is appropriate and may reduce unnecessary interventions
• High-risk pregnancies: Continuous EFM is recommended
• Abnormal findings on intermittent auscultation: Switch to continuous EFM

The decision should be based on risk assessment, available resources, and patient preferences, with the understanding that continuous EFM may become necessary if clinical situations warrant 1.