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An Introduction to Cardiotocography – “CTG”. Max Brinsmead PhD FRANZCOG July 2012. A Normal Antenatal CTG. Features of a CTG. Baseline Short term variability Accelerations Decelerations Response to stimuli Contractions Fetal movements Other. Baseline Fetal Heart Rate.

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an introduction to cardiotocography ctg

An Introduction to Cardiotocography – “CTG”

Max Brinsmead PhD FRANZCOG

July 2012

features of a ctg
Features of a CTG
  • Baseline
  • Short term variability
  • Accelerations
  • Decelerations
  • Response to stimuli
      • Contractions
      • Fetal movements
      • Other
baseline fetal heart rate
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
accelerations
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)
short term variability or beat to beat variability with a scalp clip
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
decelerations
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
abnormal ctg features
Abnormal CTG Features
  • Reduced STV
  • No accelerations
  • Decelerations after most contractions with a slow return to baseline
in practice a ctg is best regarded as a screening tool
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
the rcog classification of ctgs
The RCOG Classification of CTGs
  • Normal = all 4 features are reassuring
  • Suspicious = One non reassuring feature
  • Pathological = Two or more non reassuring features or a abnormal pattern
non reassuring features of a ctg
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
a ctg is abnormal when
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