Fetal Heart Tracing

📈 Fetal Heart Tracing: A Systematic Clinical Approach

This section provides a structured overview of fetal heart rate (FHR) monitoring, a critical aspect of intrapartum surveillance. Proper interpretation of FHR patterns enables early identification of fetal distress and guides timely obstetric intervention.

We will examine the four fundamental components of FHR interpretation—baseline rate, variability, accelerations, and decelerations—followed by categorization criteria and clinical responses.

Baseline Heart Rates

Normal: 110–160 bpm
Bradycardia: <110 bpm
Tachycardia: >160 bpm

Variability

Defined as irregular fluctuations in FHR amplitude and frequency around the baseline.

Absent: Suggests severe fetal acidemia
Minimal (<6 bpm): Associated with hypoxia, opioids, magnesium, or fetal sleep
Normal (6–25 bpm): Reassuring
Marked (>25 bpm): May indicate hypoxia; can be a prelude to worsening variability
Sinusoidal: Smooth wave-like pattern with frequency of 3–5 cycles/min; associated with severe fetal anemia

Accelerations

Abrupt rise in FHR of ≥15 bpm lasting ≥15 seconds but less than 2 minutes. Considered reassuring and typically indicates fetal well-being.

Decelerations

Defined as decreases in FHR below the baseline. Their classification depends on timing and duration relative to uterine contractions:

Type	Description	Cause
Early	Gradual onset and return; mirrors contraction	Head compression
Late	Begins after contraction peak, returns to baseline after contraction ends	Uteroplacental insufficiency
Variable	Abrupt drop >15 bpm, duration 15 sec–2 min	Cord compression

Mnemonic - "VEaL CHoP":
Variable = Cord compression
Early = Head compression
Late = Placental insufficiency
Accelerations = Okay

Categorizing Fetal Heart Tracings

FHR tracings are grouped into three categories based on baseline, variability, and decelerations.

Category	Description
I	Normal baseline (110–160 bpm) Moderate variability No late or variable decelerations +/- Early decelerations or accelerations
II	Not I or III. Includes minimal/marked variability, prolonged or recurrent variable decelerations, bradycardia with variability, etc.
III	Absent variability with: - Recurrent late decelerations - Recurrent variable decelerations - Bradycardia - Sinusoidal pattern

Clinical Action: Category II and III patterns require investigation and corrective measures (e.g., repositioning, fluid bolus, stopping oxytocin, oxygen, cesarean delivery if unresolved).