Intrapartum Cardiotocography Interpretation
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Direct answer
Intrapartum cardiotocography is the continuous recording of fetal heart rate alongside uterine contractions, interpreted by assessing baseline rate, variability, accelerations and decelerations. A reassuring trace has a baseline of 110 to 160 bpm with moderate variability and accelerations, while absent variability with recurrent late or variable decelerations signals fetal compromise. Interpretation uses a three-category approach, and the trace is judged alongside the clinical context rather than on one feature alone.
What you must remember
- Baseline rate: the average fetal heart rate over about ten minutes, excluding accelerations, decelerations and marked variability, with a normal range of 110 to 160 bpm.
- Baseline variability: absent is undetectable, minimal is 5 bpm or less, moderate is 6 to 25 bpm, and marked is more than 25 bpm.
- Accelerations: a rise of 15 bpm or more lasting 15 seconds or more, which is a reassuring feature.
- Early decelerations: a gradual fall and recovery that mirror the contraction, caused by fetal head compression and considered benign.
- Late decelerations: a gradual onset and recovery after the peak of the contraction, signalling uteroplacental insufficiency.
- Variable decelerations: an abrupt onset with variable shape and timing, caused by umbilical cord compression, and needing prompt action when recurrent.
- Category approach: Category I is normal, Category II is indeterminate and Category III is abnormal and needs urgent action.
Comparing the three types of deceleration
Decelerations are the feature examiners test most, and a table that separates the three types makes the differences easy to fix in memory. Each type is named by its timing against the contraction, which is the first thing to check on the trace.
| Feature | Early | Late | Variable |
|---|---|---|---|
| Onset | Gradual | Gradual | Abrupt |
| Timing | Matches the contraction peak | Starts after the peak | Unrelated to contractions |
| Cause | Head compression | Uteroplacental insufficiency | Cord compression |
| Shape | Symmetrical | Symmetrical, delayed | Variable, often V or W |
Early decelerations are generally benign, late decelerations are the warning sign, and variable decelerations are judged by their depth, duration and how often they recur. Recurrent late or variable decelerations with reduced variability is the combination that moves a trace into the abnormal category.
A structured description works best in an examination answer. Describe the trace in the order of baseline, variability, accelerations and decelerations, because the category follows from those four features together. Single labels such as reassuring or pathological earn less credit than a reasoned description.
Where the exam tries to catch you
Interpretation questions test the timing of decelerations and the category that a combination of features places a trace in.
- Trap: calling every deep deceleration late Correct: late decelerations begin after the contraction peak, while early ones mirror the contraction, so timing decides the type.
- Trap: reading a sinusoidal pattern as normal variability Correct: a sinusoidal pattern is abnormal and can signal severe fetal anaemia or compromise, so it needs urgent action.
- Trap: treating a Category II trace as reassuring Correct: Category II is indeterminate and needs review, reassessment and correction of causes such as maternal position or hypotension.
Frequently asked questions
What is the normal baseline fetal heart rate on intrapartum cardiotocography?
The normal baseline fetal heart rate on intrapartum cardiotocography is 110 to 160 bpm. It is measured as an average over about ten minutes, excluding accelerations and decelerations. A baseline outside this range needs assessment for fetal distress or maternal causes.
How is baseline variability graded on cardiotocography?
Baseline variability is graded as absent, minimal, moderate or marked, with minimal at 5 bpm or less and moderate at 6 to 25 bpm. Moderate variability is the reassuring pattern, while absent variability with recurrent decelerations is abnormal. The grading is made over a defined period of the trace.
What distinguishes late from variable decelerations on cardiotocography?
Late decelerations begin gradually and recover after the contraction peak, pointing to uteroplacental insufficiency. Variable decelerations begin abruptly with a variable shape and timing, pointing to umbilical cord compression. Both can occur on the same trace, and their recurrence drives management.
Which trace category requires urgent action in labour?
A Category III trace requires urgent action, and it includes absent variability with recurrent late decelerations, recurrent variable decelerations or bradycardia. A sinusoidal pattern is also abnormal. Action includes repositioning the woman, correcting hypotension, stopping oxytocin and assessing whether delivery is needed.
What is an acceleration on intrapartum cardiotocography?
An acceleration is a rise in fetal heart rate of at least 15 bpm lasting at least 15 seconds above the baseline. Its presence is reassuring and suggests a fetus with an adequate oxygen supply. Accelerations are assessed alongside variability when the trace is classified.