Classification of Electronic Fetal Monitoring (EFM) Tracings
Electronic Fetal Monitoring (EFM) tracings are classified into three categories according to the National Institute of Child Health and Human Development (NICHD) system: Category I (normal), Category II (indeterminate), and Category III (abnormal), with specific management protocols for each category. 1, 2
Category I: Normal
- Definition: Reassuring pattern indicating normal fetal acid-base status
- Characteristics:
- Normal baseline FHR (110-160 bpm)
- Moderate baseline variability (6-25 bpm)
- Accelerations present or absent
- Late or variable decelerations absent
- Management: Continue current monitoring method (structured intermittent auscultation or continuous EFM) 1
Category II: Indeterminate
- Definition: Cannot be classified as either normal or abnormal; requires increased surveillance
- Characteristics (any of the following):
- Baseline FHR changes:
- Bradycardia (<110 bpm) not accompanied by absent variability
- Tachycardia (>160 bpm)
- Variability changes:
- Minimal variability
- Absent variability not accompanied by decelerations
- Marked variability
- No FHR accelerations after fetal stimulation
- FHR decelerations without absent variability:
- Variable decelerations
- Late decelerations
- Baseline FHR changes:
- Management:
Category III: Abnormal
- Definition: Abnormal pattern indicating possible fetal acidemia
- Characteristics (either):
- Absent baseline FHR variability with:
- Recurrent late decelerations, OR
- Recurrent variable decelerations, OR
- Bradycardia
- Sinusoidal FHR pattern
- Absent baseline FHR variability with:
- Management:
Clinical Significance and Interpretation
Category I
- Indicates normal fetal well-being
- Associated with normal fetal pH
- Requires routine monitoring 1
Category II
- Represents approximately 80% of all tracings during labor 3
- Requires careful evaluation and increased surveillance
- Associated with 5-fold higher risk of low 1-minute Apgar scores compared to Category I 4
- Certain patterns (recurrent late or variable decelerations) are more predictive of neonatal acidemia 3
- May require intrauterine resuscitation techniques 1, 2
Category III
- Indicates uteroplacental insufficiency, ongoing fetal hypoxia, and potential acidemia
- High risk for adverse neonatal outcomes
- Requires immediate intervention and expedited delivery 1, 2
Important Considerations
- For pregnancies ≥32 weeks, an acceleration is defined as an increase in FHR of 15 beats/minute above baseline lasting for 15 seconds 2
- For pregnancies <32 weeks, an acceleration is defined as 10 beats/minute above baseline lasting for 10 seconds 2
- Category II tracings require stratification based on specific features, as some patterns carry higher risk than others 5
- The speed of onset of intrapartum hypoxia (acute, subacute, or gradually evolving) and preexisting uteroplacental insufficiency are crucial factors in determining outcomes 6
- Proper documentation of all interventions and their timing is essential for establishing appropriate care 2
- Cord blood gases should be obtained after delivery when abnormal FHR tracings prompted intervention 2
Common Pitfalls to Avoid
- Failing to recognize the progression from Category II to Category III patterns
- Delaying intervention for persistent Category II patterns with concerning features
- Not implementing intrauterine resuscitation measures promptly
- Overlooking the clinical context (labor progress, fetal size, meconium, inflammation)
- Not documenting interventions and their timing properly
This classification system provides a standardized framework for interpreting and managing EFM tracings, helping to identify fetuses at risk of acidemia and guide appropriate interventions to improve outcomes.