What are the recommended interpretation and management steps for cardiotocography (CTG) in a term (≥37 weeks) laboring patient, including how to handle Category I, Category II, and Category III tracings and any maternal conditions such as pre‑eclampsia, diabetes, or anemia?

CTG Guidelines and Management in Term Labor

CTG Classification Systems

Use the three-tier NICHD classification system to categorize all intrapartum CTG tracings as Category I (normal), Category II (indeterminate), or Category III (abnormal), with management decisions based on the specific category and clinical context. 1

Category I (Normal) – Reassuring

Category I tracings include all of the following features and require only routine labor management: 1

• Baseline fetal heart rate (FHR): 110–160 bpm 1
• Baseline variability: Moderate (6–25 bpm) 1
• Accelerations: Present or absent 1
• Decelerations: None, or early decelerations only 1

Management: Continue routine labor care with intermittent auscultation or continuous monitoring per institutional protocol. 1

Category II (Indeterminate) – Requires Increased Surveillance

Category II encompasses all tracings that do not meet Category I or III criteria, including: 1

• Baseline FHR: Bradycardia (< 110 bpm) not accompanied by absent variability, or tachycardia (> 160 bpm) 1
• Baseline variability: Minimal (≤ 5 bpm), absent without recurrent decelerations, or marked (> 25 bpm) 1
• Accelerations: Absence of induced accelerations after fetal stimulation 1
• Decelerations: Recurrent variable decelerations with minimal or moderate variability, prolonged decelerations (≥ 2 minutes but < 10 minutes), recurrent late decelerations with moderate variability, or variable decelerations with slow return to baseline or "overshoots" 1

Management approach for Category II tracings: 1, 2

1. Identify and correct reversible causes: Maternal hypotension, uterine tachysystole, maternal hypoxia 2
2. Implement intrauterine resuscitation measures: 2
   • Reposition mother (left lateral position preferred)
   • Administer IV fluid bolus if hypovolemia suspected
   • Reduce or discontinue oxytocin if tachysystole present
   • Administer supplemental oxygen (though benefit is debated)
   • Consider tocolysis for persistent tachysystole
3. Increase monitoring frequency: Continuous CTG with more frequent clinical assessment 1
4. Consider ancillary tests if pattern persists: Fetal scalp stimulation to elicit acceleration, or fetal scalp blood sampling where available (pH > 7.25 reassuring) 2
5. Prepare for expedited delivery if pattern deteriorates to Category III or fails to improve despite interventions 1, 2

Category III (Abnormal) – Requires Immediate Action

Category III tracings include either: 1

• Absent baseline variability AND any of: 1
  • Recurrent late decelerations
  • Recurrent variable decelerations
  • Bradycardia
• Sinusoidal pattern (smooth, sine wave-like undulating pattern, cycle frequency 3–5 per minute, amplitude 5–15 bpm above and below baseline, lasting ≥ 20 minutes) 1

Management: 1, 2

1. Initiate immediate intrauterine resuscitation (as outlined above for Category II)
2. Prepare for urgent delivery (vaginal if imminent, otherwise cesarean section)
3. Notify anesthesia, pediatrics, and operating room staff
4. Document interventions and decision-making clearly
5. Delivery should occur as rapidly as safely possible – typically within 30 minutes of recognition if intrauterine resuscitation fails 2

Physiological Interpretation of CTG Features

Understand the physiological basis of FHR patterns rather than relying solely on pattern recognition, as this reduces unnecessary interventions and improves outcomes. 2

Baseline Variability – The Most Important Feature

• Moderate variability (6–25 bpm) indicates intact neurological pathways and excludes significant acidemia at that moment 2
• Reduced or absent variability may indicate fetal sleep cycles (typically < 40 minutes), maternal medications (opioids, magnesium sulfate, benzodiazepines), fetal neurological immaturity (< 28 weeks), or evolving hypoxia/acidemia 3, 2
• Saltatory (marked) variability (> 25 bpm) may represent acute compensatory response to hypoxic stress 2, 4

Decelerations – Mechanism Matters

• Early decelerations: Gradual decrease and return to baseline, mirror contractions, nadir coincides with contraction peak – caused by fetal head compression, benign 2
• Variable decelerations: Abrupt decrease (≥ 15 bpm below baseline, lasting ≥ 15 seconds but < 2 minutes), variable timing relative to contractions – caused by umbilical cord compression, concerning if recurrent with reduced variability or slow return to baseline 2
• Late decelerations: Gradual decrease and return, onset after contraction begins, nadir after contraction peak – indicate uteroplacental insufficiency and potential hypoxia, especially concerning with reduced variability 2
• Prolonged decelerations: Decrease ≥ 15 bpm below baseline lasting ≥ 2 minutes but < 10 minutes – require immediate assessment and intervention 2, 5

Accelerations

• Presence of accelerations (≥ 15 bpm above baseline for ≥ 15 seconds) indicates fetal well-being and intact neurological function 2
• Absence of accelerations alone is not pathological but requires correlation with other CTG features 1

Special Considerations for Maternal Conditions

Pre-eclampsia

Women with pre-eclampsia require continuous intrapartum CTG monitoring due to increased risk of placental insufficiency and fetal compromise. 1, 6

• Initiate continuous CTG at admission to labor ward 1
• Lower threshold for intervention with Category II patterns given underlying uteroplacental dysfunction 1
• Maintain blood pressure control during labor (target systolic 110–140 mmHg, diastolic ≤ 85 mmHg) to optimize uteroplacental perfusion 6, 7
• Continue magnesium sulfate throughout labor and for 24 hours postpartum if administered for seizure prophylaxis 6, 7
• Consider earlier recourse to cesarean delivery if Category II patterns persist despite intrauterine resuscitation, particularly with severe features or fetal growth restriction 1, 6

Diabetes Mellitus

Diabetic pregnancies require continuous intrapartum monitoring due to increased risks of macrosomia, shoulder dystocia, and metabolic complications. 1

• Maintain tight glycemic control during labor (target glucose 4–7 mmol/L or 72–126 mg/dL) to reduce risk of neonatal hypoglycemia 1
• Be alert for baseline tachycardia which may indicate maternal hyperglycemia or infection 2
• Increased vigilance for shoulder dystocia if macrosomia present – consider early recourse to cesarean delivery if labor dystocia develops 1

Anemia

Maternal anemia (hemoglobin < 110 g/L or < 11 g/dL) reduces oxygen-carrying capacity and may compromise fetal oxygenation during labor stress. 1

• Continuous CTG monitoring recommended for moderate-to-severe anemia (Hb < 90 g/L or < 9 g/dL) 1
• Lower threshold for intervention with Category II patterns given reduced maternal oxygen reserve 2
• Optimize maternal oxygenation with supplemental oxygen if CTG abnormalities develop 2
• Avoid prolonged second stage – consider operative vaginal delivery if maternal exhaustion develops 1

Preterm Considerations (< 37 Weeks)

CTG interpretation differs in preterm fetuses due to neurological immaturity, requiring adjusted expectations for baseline variability and accelerations. 3

Gestational Age-Specific Features

• 25–30 weeks: Expect more baseline tachycardia (up to 170 bpm may be normal), reduced variability (3–5 bpm may be acceptable), fewer accelerations, and longer sleep cycles (up to 60 minutes) 3, 8
• 31–36 weeks: Transitional patterns with gradual maturation toward term features 3
• Reduced variability alone is less concerning in preterm fetuses if other features (baseline, accelerations when present) are reassuring 3

Management Adjustments

• Extend observation period before diagnosing absent variability (up to 60–90 minutes) to account for longer sleep cycles 3
• Use fetal scalp stimulation to differentiate sleep from hypoxia – elicited acceleration is reassuring 3
• Consider computerized CTG analysis (e.g., Oxford System) to reduce inter-observer variability in preterm tracings 5

Common Pitfalls and How to Avoid Them

High False-Positive Rate

CTG has approximately 60% false-positive rate for predicting fetal hypoxia, leading to unnecessary interventions if used in isolation. 2

• Always correlate CTG findings with clinical context: maternal condition, labor progress, risk factors 2
• Use ancillary tests (fetal scalp stimulation, scalp pH if available) to clarify equivocal tracings 2
• Avoid cesarean delivery for Category II tracings that respond to intrauterine resuscitation 2

Inter-Observer Variability

Visual CTG interpretation has significant inter- and intra-observer variability, even among experienced clinicians. 2

• Use structured classification systems (NICHD three-tier) consistently 1
• Document specific features systematically: baseline, variability, accelerations, decelerations 1
• Seek second opinion for Category II/III tracings when time permits 2
• Consider computerized analysis systems to supplement visual interpretation 5

Failure to Act on Category III Tracings

Delayed intervention for Category III tracings is associated with worse neonatal outcomes. 2

• Recognize Category III patterns immediately: absent variability with recurrent decelerations or bradycardia, or sinusoidal pattern 1
• Initiate intrauterine resuscitation while preparing for delivery – do not delay 2
• Aim for delivery within 30 minutes if pattern persists despite resuscitation 2

Over-Reliance on CTG Alone

CTG is a screening tool with limited positive predictive value (approximately 30%) for intrapartum hypoxia. 2

• Integrate CTG findings with clinical assessment: maternal vital signs, labor progress, risk factors, fetal movement 2
• Do not ignore reassuring clinical features (normal labor progress, clear amniotic fluid, absence of risk factors) when CTG shows isolated Category II features 2
• Conversely, do not ignore concerning clinical features (thick meconium, maternal fever, sentinel events) even with Category I tracing 5

Practical Algorithm for CTG Management

1. Classify tracing using NICHD three-tier system 1
2. Category I: Continue routine care 1
3. Category II: 1, 2
   • Identify and correct reversible causes
   • Implement intrauterine resuscitation
   • Increase monitoring frequency
   • Consider ancillary tests if pattern persists
   • Prepare for expedited delivery if deterioration occurs
4. Category III: 1, 2
   • Immediate intrauterine resuscitation
   • Prepare for urgent delivery
   • Notify team (anesthesia, pediatrics, OR)
   • Deliver as rapidly as safely possible
5. Document clearly: Specific CTG features, interventions, clinical reasoning 2