How is a non-reassuring (NR) heart rate pattern identified in Obstetrics (ObGyn)?

Identification of Non-Reassuring Fetal Heart Rate Patterns

Non-reassuring fetal heart rate patterns are identified using the NICHD three-category classification system, where Category III patterns (abnormal) represent true non-reassuring tracings requiring immediate intervention, while Category II patterns (indeterminate) warrant increased surveillance and may evolve into non-reassuring patterns. 1

Systematic Approach: DR C BRAVADO Mnemonic

The structured evaluation of fetal heart rate tracings follows this algorithmic approach 1:

D-R: Determine Risk

• Assess clinical context (high, medium, or low-risk pregnancy) 1

C: Contractions

• Evaluate rate, rhythm, frequency, duration, intensity, and resting tone 1
• Identify tachysystole (>5 contractions per 10 minutes averaged over 30 minutes) 1

BRA: Baseline Rate

• Normal: 110-160 bpm 1
• Bradycardia: <110 bpm 1
• Tachycardia: >160 bpm 1

V: Variability (Most Critical Parameter)

• Moderate variability (6-25 bpm): Reassuring, predicts absence of fetal acidemia 1
• Absent variability: Non-reassuring, especially when combined with decelerations 1
• Minimal variability: May indicate fetal sleep cycles (20-40 minutes), medications, or evolving hypoxia 1

A: Accelerations

• Presence of accelerations: Reassuring regardless of other FHR patterns 2
• Absence after fetal stimulation: Suggests possible fetal hypoxia or acidemia 1

D: Decelerations

• Early decelerations: Benign, mirror contractions, nadir coincides with contraction peak 1
• Variable decelerations: Usually benign unless atypical features present (late onset, loss of shoulders, slow recovery) 1
• Late decelerations: Non-reassuring, onset delayed after contraction begins, nadir after contraction peak, indicates uteroplacental insufficiency 1, 3
• Prolonged decelerations: Last 2-10 minutes, require immediate assessment 1

NICHD Three-Category Classification System

Category I (Normal/Reassuring) 1

• Normal baseline FHR (110-160 bpm)
• Moderate baseline variability
• Late or variable decelerations absent
• Accelerations present or absent
• Management: Continue current monitoring 1

Category II (Indeterminate) 1

Includes all tracings not categorized as I or III, representing the majority (>50%) of intrapartum tracings 1:

• Bradycardia without absent variability 1
• Tachycardia 1
• Minimal, absent (without decelerations), or marked variability 1
• Absence of accelerations after fetal stimulation 1
• Recurrent variable decelerations with moderate variability 1
• Prolonged decelerations ≥2 minutes but <10 minutes 1
• Recurrent late decelerations with moderate variability 1
• Management: General measures (position change, oxygen, IV fluids, vaginal exam, assess maternal vitals), consider discontinuing oxytocin, consider expedited delivery if abnormalities persist 1, 3

Category III (Abnormal/Non-Reassuring) 1

These are the true non-reassuring patterns requiring immediate intervention:

• Absent baseline variability WITH:
  • Recurrent late decelerations, OR 1
  • Recurrent variable decelerations, OR 1
  • Bradycardia 1
• Sinusoidal pattern (smooth undulating sine wave, amplitude 10 bpm, 3-5 cycles/minute, lasting ≥20 minutes) 1
• Management: Discontinue oxytocin immediately, expedite delivery by operative vaginal or cesarean delivery 1

Research-Based Reassuring vs. Non-Reassuring Distinction

Reassuring patterns (84% of tracings) predict normal outcomes 2:

• No FHR abnormalities, mild variable decelerations, decreased variability, mild bradycardia, or accelerations present predict 5-minute Apgar ≥7 in 99.7% and cord pH ≥7.15 in 96.9% 2
• Accelerations are reassuring regardless of other FHR patterns 2

Non-reassuring patterns (increase risk 50-fold) 2:

• Both without accelerations AND have:
  • Tachycardia, OR 2
  • Prolonged bradycardia, OR 2
  • Severe variable decelerations, OR 2
  • Late decelerations, OR 2
  • Combination of these patterns 2

Critical Pitfalls to Avoid

• Fetal sleep cycles (20-40 minutes) commonly cause temporary decreased variability; extend observation before declaring pattern non-reassuring 1
• Medications (analgesics, anesthetics, magnesium sulfate) can decrease variability without indicating fetal compromise 1
• Isolated findings without absent variability are generally not non-reassuring; the combination of absent variability with decelerations or bradycardia defines true non-reassuring patterns 1, 2
• Subtle late decelerations can be difficult to visualize; use a straight edge along the baseline to detect shallow patterns 1
• Variable decelerations are the predominant type in most intrapartum recordings and are usually benign unless atypical features present 1, 4