According to NICE guidelines, when is continuous cardiotocography indicated in labour, how should the three‑category system be interpreted, and what management is recommended for each category?

NICE Guidelines on Cardiotocography (CTG) in Labour

Indications for Continuous CTG Monitoring

Continuous electronic fetal monitoring should be used for high-risk patients, while structured intermittent auscultation is appropriate for low-risk labours with a 1:1 nurse-to-patient ratio. 1

High-Risk Factors Requiring Continuous CTG:

• Maternal risk factors including pre-existing medical conditions, pregnancy complications (preeclampsia, diabetes), or intrapartum fever/chorioamnionitis 1
• Fetal risk factors such as intrauterine growth restriction, oligohydramnios, or abnormal umbilical artery Doppler studies 2
• Intrapartum complications including oxytocin augmentation, epidural analgesia, meconium-stained liquor, or abnormal findings on intermittent auscultation 1
• Previous caesarean section or other uterine surgery 1

Low-Risk Labour Monitoring:

• Structured intermittent auscultation should be performed at specific intervals: every 15 minutes in active first stage and every 5 minutes in second stage 1
• Auscultation should occur for at least 60 seconds after a contraction to detect decelerations, though this methodology may miss late decelerations that nadir during contractions 3
• Admission CTG is not recommended for low-risk women as it increases caesarean section rates by approximately 20% without improving perinatal outcomes 4

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Three-Category CTG Classification System

The National Institute of Child Health and Human Development established a standardized three-tier classification system for interpreting CTG tracings 1, 5:

Category I (Normal/Reassuring):

• Baseline fetal heart rate 110-160 bpm 1
• Moderate baseline variability (6-25 bpm amplitude) 1
• Presence of accelerations (≥15 bpm for ≥15 seconds) 1
• No late or variable decelerations 1
• Early decelerations may be present 1

Management: Continue routine monitoring; no intervention required 1

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Category II (Indeterminate/Suspicious):

This encompasses all tracings not classified as Category I or III, including 1, 5:

• Baseline bradycardia (<110 bpm) without absent variability 1
• Baseline tachycardia (>160 bpm) 1
• Minimal baseline variability (amplitude <5 bpm) 1
• Absent baseline variability without recurrent decelerations 1
• Marked baseline variability (>25 bpm) 1
• Absence of induced accelerations after fetal stimulation 1
• Recurrent variable decelerations with minimal or moderate variability 1
• Prolonged decelerations (≥2 minutes but <10 minutes) 1
• Recurrent late decelerations with moderate variability 5

Management Algorithm:

1. Implement intrauterine resuscitation measures immediately 5:

   • Discontinue oxytocin if being administered 5
   • Position mother in left lateral decubitus position to optimize uterine blood flow 1, 6
   • Establish or increase IV fluid administration with physiologic solutions 5
   • Administer supplemental oxygen to mother 6
   • Perform vaginal examination to exclude cord prolapse or assess cervical change 5
   • Check maternal vital signs to identify hypotension or other contributing factors 5

2. Increase surveillance frequency with continuous monitoring 5

3. Prepare for expedited delivery if abnormalities persist or worsen despite resuscitation measures 5

4. Do not rely on fetal scalp stimulation or acoustic stimulation as substitutes for delivery when persistent Category II patterns indicate fetal compromise 5

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Category III (Abnormal/Pathological):

Requires immediate expeditious delivery 5:

• Absent baseline variability with any of the following 1, 5:
  • Recurrent late decelerations 5
  • Recurrent variable decelerations 1
  • Bradycardia 1
• Sinusoidal pattern (smooth, undulating sine wave pattern with 10 bpm amplitude, 3-5 cycles/minute, lasting ≥20 minutes) 1

Management:

1. Activate emergency protocols immediately for caesarean delivery with decision-to-delivery interval within 25 minutes 6
2. Continue intrauterine resuscitation measures while preparing for delivery 5, 6
3. Notify anesthesiology and neonatology teams urgently 6
4. Do not delay delivery for additional testing or prolonged resuscitation attempts 5

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Systematic CTG Interpretation: DR C BRAVADO Mnemonic

Use this structured approach for every CTG assessment 1:

• DR (Determine Risk): Assess maternal and fetal risk factors 1
• C (Contractions): Evaluate frequency, duration, intensity (normal = ≤5 contractions per 10 minutes) 1
• BRA (Baseline Rate): Identify baseline FHR (normal 110-160 bpm) 1
• V (Variability): Assess amplitude (absent, minimal, moderate, or marked) 1
• A (Accelerations): Note presence or absence of spontaneous accelerations 1
• D (Decelerations): Classify type (early, variable, late, or prolonged) 1
• O (Overall Assessment): Categorize as I, II, or III and implement appropriate management 1

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Understanding Deceleration Patterns

Early Decelerations:

• Gradual decrease (≥30 seconds from onset to nadir) that mirrors uterine contractions 1
• Nadir occurs simultaneously with contraction peak 1
• Rarely fall below 100 bpm and represent fetal head compression 1
• Benign finding requiring no intervention 1

Late Decelerations:

• Gradual decrease (≥30 seconds from onset to nadir) with delayed timing relative to contractions 1, 5
• Nadir occurs after the contraction peak, indicating uteroplacental insufficiency 5
• Represent fetal hypoxemia and potential acidosis, particularly when accompanied by absent or minimal variability 5
• Require immediate intrauterine resuscitation and preparation for delivery 5

Variable Decelerations:

• Abrupt decrease (<30 seconds from onset to nadir) with variable timing and shape 1
• Usually indicate umbilical cord compression 1
• Management depends on severity, frequency, and associated variability 1

Prolonged Decelerations:

• Decrease in FHR ≥15 bpm lasting ≥2 minutes but <10 minutes 1
• Require immediate assessment and intrauterine resuscitation 5

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Critical Clinical Pitfalls

Avoid Admission CTG in Low-Risk Women:

Despite widespread use, admission CTG increases caesarean section rates without improving perinatal outcomes and should not be performed routinely 4. Studies show 82% of low-risk women receive admission CTG contrary to guidelines 7.

Recognize Limitations of Intermittent Auscultation:

Current methodology of auscultating for 60 seconds after contractions may miss late decelerations that reach their nadir before contraction ends, potentially misinterpreting the recovery phase as normal 3. Consider auscultating before and after contractions to establish baseline and detect decelerations 3.

Understand CTG's High False-Positive Rate:

CTG has only 30% positive predictive value for fetal hypoxia and 60% false-positive rate 8. This explains increased operative delivery rates without corresponding improvement in cerebral palsy or perinatal mortality 1, 8.

Avoid Tachysystole:

More than 5 contractions in 10 minutes (averaged over 30 minutes) compromises uteroplacental blood flow 1. The term "hyperstimulation" is obsolete and should not be used 1.

Maintain Continuous Monitoring for High-Risk Patients:

Studies show 9% of high-risk women are not monitored with continuous CTG as recommended, representing a significant patient safety concern 7.

Recognize Factors Affecting Variability:

Fetal sleep cycles (20-40 minutes), maternal medications (analgesics, anesthetics, magnesium sulfate), and prematurity can cause decreased variability without fetal compromise 1. However, loss of variability with late or variable decelerations significantly increases risk of fetal acidosis 1.