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Interpretation of abnormal CTG
pattern
Ngee Wey Yi & Pariksit Rao
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Categorisation of FHR Features
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Categorisation of FHR Patterns
Normal A CTG where all 4features fall into thereassuring category.
Suspicious A CTG whose features fall into 1of the non-
reassuring categories & the remainder arereassuring.
Pathological A CTG whose features fall into 2 or more non-
reassuring categories or 1or more abnormal
categories.
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Baseline rate
Normal = 110160bpm
Bradycardia (moderate) = 100109bpm
Bradycardia (abnormal) = < 100 bpm
Tachycardia (moderate) = 161180 bpm
Tachycardia (abnormal) = >180 bpm (RCOG)
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Foetal Tachycardia
It can be caused by:
Foetal hypoxia
Chorioamnionitisif maternal fever also present
Foetal or Maternal Anaemia
Foetal tachyarrhythmia
Foetal Bradycardia
Post-date gestation
Occiput posterior or transverse presentations
Prolonged cord compression
Cord prolapse
Epidural & Spinal Anaesthesia
Maternal seizures Rapid foetal descent
If the cause cannot be identified and corrected, immediate delivery isrecommended
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Variability
Refers to the variation of fetal heart rate fromone beat to the next.
Greater than 5bpm and less than 25bpm
Should settle after about 10 mins when the
foetus returns to normal O2 levels
Increased variability is often seen following an
acute hypoxic event.
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To calculate variability you look at how much the peaks & troughs of the
heart rate deviate from the baseline rate (in bpm)
Reassuring 5 bpm
Non-reassuring< 5bpm for between 40-90 minutes Abnormal< 5bpm for >90 minutes
Reduced variability can be caused by:
Foetus sleeping -this should last no longer than 40 minutes most
common cause Foetal acidosis (due to hypoxia)more likely if late decelerations also
present
Foetal tachycardia
Drugsopiates, benzodiazipines, methyldopa, magnesium sulphate
Prematurityvariability is reduced at earlier gestation (
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Acceleration
Accelerations are an abrupt increase in baselineheart rate of >15 bpm for >15 seconds
The presence of accelerations is reassuring
Antenatally there should be at least 2
accelerations every 15 minutes
Accelerations occurring alongside uterine
contractions is a sign of a healthy foetusHowever the absence of accelerations with an
otherwise normal CTG is of uncertain significance
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Deceleration
Decelerations are an abrupt decrease in baselineheart rate of >15 bpm for >15 seconds.
4 types: Early
LateVariabletypical and atypical
Prolonged
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Early deceleration
Early decelerations start when uterine contraction begins & recover
when uterine contraction stops.
This is due to increased foetal intracranial pressure causing increased
vagal tone.
It therefore quickly resolves once the uterine contraction ends &
intracranial pressure reduces.
This type of deceleration is therefore considered to be physiological &
not pathological.
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Late deceleration
Begin at the peak of uterine contraction & recover after
The contraction ends.
Indicates there is insufficient blood flow through the uterus & placentacausing foetal hypoxia & acidosis
The presence of late decelerations is taken seriously & foetal blood sampling
for pH is indicated. If foetal blood pH is acidotic it indicates significant foetal
hypoxia & the need for emergency C-section
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Variable deceleration
2 types: Typical
Atypical
Repetitive or intermittent Often mimic letters of the alphabet
U V W M
Reflect some degree of umbilical cord impingement
Often seen when liquor volume is
Prolonged Decelerations
FHR falls for > 3 minutes
If it lasts between 2-3 minutes it is classed as Non-Reasurring
If it lasts longer than 3 minutes it is immediately classed as Abnormal Action must be taken quicklye.g. Foetal blood sampling / emergency
C-section
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SinusoidalVery rare pattern
Sign of a dying baby
No beat to beat variability
A sinusoidal pattern indicates:
Severe foetal hypoxia
Severe foetal anaemiaFoetal/Maternal Haemorrhage
Immediate C-section is indicated for this kind of pattern.