How to arrive to a pathological and suspicious and normal ctg

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CTG cardiotocography classification normal suspicious pathological fetal heart rate

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Here is a comprehensive guide to CTG (cardiotocography) classification using the FIGO 2015 guidelines — the current international standard that divides tracings into Normal, Suspicious, and Pathological.

CTG Classification: Normal, Suspicious, and Pathological

Step 1 — Evaluate the Four Core CTG Features

Before classifying, assess each of these independently:

Feature	What to measure
Baseline FHR	Mean FHR over a 10-min window (excluding accelerations/decelerations)
Variability	Amplitude of beat-to-beat fluctuation around the baseline
Accelerations	Transient rises in FHR ≥15 bpm lasting ≥15 sec
Decelerations	Transient falls in FHR — classify by timing and shape

Step 2 — Define Each Feature (Normal Ranges)

Baseline FHR

Normal: 110–160 bpm
Tachycardia: >160 bpm
Bradycardia: <110 bpm (100–110 bpm = intermediate/suspicious zone)

Baseline Variability

Normal: 5–25 bpm amplitude
Reduced: <5 bpm
Increased (saltatory): >25 bpm
Sinusoidal: smooth, undulating sine-wave pattern ≥30 min — always pathological

Accelerations

Presence = reassuring (fetus without hypoxia/acidosis)
Absence during labour is not itself pathological, but is of uncertain significance

Decelerations — Types

Type	Onset	Cause	Significance
Early	Gradual, mirrors contraction	Head compression	Benign
Variable	Abrupt (<30 sec to nadir)	Cord compression	Context-dependent
Late	Gradual, begins after contraction peak; nadir >30 sec after onset	Uteroplacental insufficiency → fetal hypoxemia	Most concerning
Prolonged	Single deceleration lasting ≥2 min	Various	Duration determines severity

Step 3 — Classify the Tracing (FIGO 2015)

Feature	Normal	Suspicious	Pathological
Baseline	110–160 bpm	Lacks ≥1 normal feature, but no pathological feature	<100 bpm
Variability	5–25 bpm	Reduced <5 bpm for >50 min, or increased >25 bpm for >30 min	Sinusoidal pattern ≥30 min
Decelerations	No repetitive decelerations	Repetitive decelerations present (but don't meet pathological criteria)	Repetitive late or prolonged decelerations for >30 min (or >20 min if variability is also reduced), OR a single prolonged deceleration >5 min
Clinical meaning	No hypoxia/acidosis	Low probability of hypoxia/acidosis	High probability of hypoxia/acidosis

"Repetitive" = occurring with ≥50% of contractions over a 20–30 min window.

Step 4 — Management by Category

Classification	Action
Normal	No intervention needed for fetal oxygenation; continue monitoring
Suspicious	Correct reversible causes (maternal position, hydration, oxytocin reduction), close monitoring, consider additional fetal assessment (e.g. scalp pH/lactate, fetal pulse oximetry)
Pathological	Immediate action: correct reversible causes + additional fetal assessment OR expedite delivery. In acute situations (cord prolapse, uterine rupture, placental abruption) → immediate delivery

ACOG Three-Tier System (used in the USA)

The USA uses a parallel Category I/II/III system:

Category	Equivalent	Criteria
Category I (Normal)	Normal	Baseline 110–160 bpm, moderate variability, ± accelerations, no late/variable decelerations
Category II (Indeterminate)	Suspicious	Everything not in I or III — requires continued observation
Category III (Abnormal)	Pathological	Absent variability WITH: recurrent late decelerations, recurrent variable decelerations, bradycardia, OR sinusoidal pattern

(Barash, Clinical Anesthesia 9e)

Visual Examples

Normal vs. Suspicious CTG:

Normal CTG (left) shows high variability and multiple accelerations; Suspicious CTG (right) shows reduced variability and fewer accelerations

Left (a): Normal — high beat-to-beat variability with multiple accelerations. Right (b): Suspicious — flattened trace with reduced variability.

Pathological vs. Normal comparison:

Pathological CTG (top) shows frequent deep decelerations with minimal accelerations; Normal CTG (bottom) shows small decelerations and prominent accelerations

Top: Pathological trace (pH < 7.05) — frequent, deep decelerations, minimal accelerations. Bottom: Normal — reactive pattern with accelerations.

Pathological — deep variable decelerations:

CTG strip with deep variable decelerations reaching below 100 bpm coinciding with uterine contractions

Deep, prolonged variable decelerations (>60 bpm depth, >60 sec duration) with frequent contractions — pathological by FIGO criteria.

Key Pitfalls

Absent accelerations alone do not make a trace suspicious during labour — this is of uncertain significance
Reduced variability is only suspicious if present for >50 minutes continuously; short periods may reflect fetal sleep cycle (~20 min)
A single prolonged deceleration >5 min = pathological regardless of other features
CTG has significant inter-observer variability — the suspicious/pathological boundary has the lowest agreement among clinicians
A normal CTG effectively excludes current hypoxia/acidosis; however, suspicious and pathological traces have a high false-positive rate for metabolic acidosis

Sources: FIGO 2015 Consensus Guidelines on Intrapartum Fetal Monitoring; Barash, Cullen & Stoelting's Clinical Anesthesia 9e (Table 41-8); NICE CTG classification framework.

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