1. An Introduction to Cardiotocography – “CTG”
Max Brinsmead MB BS PhD
May 2015

2. A Normal Antenatal CTG

3. Features of a CTG Baseline Short term variability Accelerations
Decelerations
Response to stimuli
Contractions
Fetal movements
Other

4. Baseline Fetal Heart Rate
110 to 150 bpm at term
Faster in early pregnancy
Below 100 = baseline bradycardia
Below 80 = severe bradycardia
Tachycardia common with maternal fever
Tachycardia with reduced STV = early hypoxia
Look for a rising baseline

5. Accelerations Must be >15 bpm and >15 sec above baseline
Should be >2 per 15 min period
Always reassuring when present
May not occur when fetus is “sleeping”
Should occur in response to fetal movements or fetal stimulation
Non reactive periods usually do not exceed 45 min
(>90 min and no accelerations is worrying)

6. Short Term Variability (or Beat to Beat Variability with a Scalp Clip)
Should be >5 bpm
The most important feature of any CTG
Is a reflection of competing acceleratory and decelerating CNS influences on the fetal heart
And therefore represents the best measure of CNS oxygenation
Will be affected by drugs
Will be reduced in the pre term fetus

7. Decelerations Early: mirrors the contraction
Typically occurs as the head enters the pelvis and is compressed, i.e. it is a vagal response
Late: Follows every contraction and exhibits a slow return to baseline
Is quite rare but is the response of a hypoxic myocardium
Variable: Show no relationship to contractions
Mild
Moderate
Severe
In practice many “decels” or “dips” are MIXED

8. An Abnormal Antenatal CTG

9. An Abnormal Antenatal CTG cont’d

10. Abnormal CTG Features Reduced STV No accelerations
Decelerations after most contractions with a slow return to baseline

11. In Practice a CTG is best regarded as a screening tool:
High negative predictive value
>98% of fetuses with a normal CTG will be OK
Poor positive predictive value
50% of fetuses with an abnormal CTG will be hypoxic and acidotic but 50% will be OK
Therefore the CTG should always be interpreted in its clinical context
And backed by fetal blood sampling PRN

12. Non Reassuring Features of a CTG
Baseline <110>100 or >160<180
STV <5 for >40 min but <90 min
Early decelerations
Variable decelerations
A single prolonged deceleration up to 3 min

13. A CTG is abnormal when: Baseline is <100 or >180 bpm
STV is <5 for >90 min
Late decelerations are repeated
Atypical variable decelerations occur
Two prolonged decelerations for >3 min occur
Sinusoidal pattern >10 min

14. Any Questions or Comments?
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