Is One Abnormal CTG Pattern Enough to Consider it Non-Reassuring?
A single abnormal pattern on cardiotocography is sufficient to classify the tracing as non-reassuring and warrants immediate intervention or increased surveillance. You do not need multiple abnormal features present simultaneously to act on concerning CTG findings.
Understanding CTG Classification
Category 2 (indeterminate) CTG patterns represent a single concerning finding and constitute over 50% of all fetal monitoring strips 1. These patterns fall between normal and abnormal and include:
- Baseline FHR changes alone
- Minimal or absent variability by itself
- Absence of accelerations
- Any periodic or episodic decelerations 1
The presence of even one of these features is sufficient to classify the CTG as non-reassuring and triggers a management algorithm 1.
Clinical Significance of Single Abnormal Patterns
Isolated Late Decelerations
The presence of late decelerations alone indicates uteroplacental insufficiency and fetal hypoxemia requiring urgent intervention 2. Late decelerations are characterized by delayed onset after contraction begins, with the nadir occurring after the peak of the contraction 2. When late decelerations are present, immediate cesarean section is recommended as they indicate active fetal compromise 2.
Isolated Variable Decelerations
Severe variable decelerations alone increase the risk for intrapartum fetal metabolic acidemia to the same extent as late decelerations 3. When combined with tachycardia, the risk of acidemia reaches 20-25% at first fetal blood sampling and 33-49% at last sampling 3.
Isolated Reduced Variability
Isolated reduced variability without other concerning features is the exception to the rule - it is in most cases not a sign of hypoxia and does not require repetitive fetal blood sampling throughout labor if hypoxia is ruled out with one assessment 3. The median lactate concentration in cases with isolated reduced variability does not differ from the normal group 3.
Immediate Management Algorithm for Single Abnormal Pattern
When you identify one abnormal CTG pattern, implement the following steps:
Discontinue oxytocin if being administered 1
Implement general measures immediately:
- Perform vaginal examination
- Check maternal vital signs
- Administer oxygen
- Change maternal position
- Provide intravenous fluids 1
Assess fetal pH with acoustic or fetal scalp stimulation to further evaluate fetal status 1
Consider expediting delivery if abnormalities persist or worsen 1
Surveillance Frequency Based on Single Abnormal Finding
For Category 2 CTG without absent/reversed end-diastolic velocity, weekly cardiotocography testing is recommended after viability 1. However, increase frequency to twice weekly or more when Category 2 patterns are accompanied by other risk factors such as fetal growth restriction 1.
Predictive Value of Single Abnormal Patterns
A normal CTG in pregnancies with fetal growth restriction is more likely to be associated with normal perinatal outcome 4. Conversely, abnormal CTG patterns during intrapartum monitoring have high specificity and negative predictive value but low sensitivity and positive predictive value for detection of birth asphyxia 5.
Normal non-stress CTG is a reliable screening indicator of fetal wellbeing, and abnormal pregnancy outcomes were more common when initial CTG was abnormal or persistently non-reassuring 6. In the study of women presenting with reduced fetal movement, no perinatal death occurred in either group following CTG assessment 6.
Common Pitfalls to Avoid
Do not wait for multiple abnormal features to accumulate before acting - a single concerning pattern warrants intervention 1, 2. The exception is isolated reduced variability without decelerations or tachycardia, which typically does not indicate hypoxia 3.
Do not rely solely on CTG without integrating comprehensive Doppler assessment of multiple vessels when managing high-risk pregnancies 1. Avoid proceeding to immediate delivery based on Category 2 CTG alone without evidence of progressive deterioration 1.
Be aware that inter-observer agreement on CTG classification is poor (κw range 0.31-0.50), with observers agreeing best on abnormal CTG patterns (Pa range 0.28-0.36) 7. This underscores the importance of having clear action thresholds for single abnormal findings rather than waiting for consensus on multiple features.