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Understanding Cardiotocography – “CTGs”

Understanding Cardiotocography – “CTGs”. A Normal Antenatal CTG. Baseline Short term variability Accelerations Decelerations Response to stimuli Contractions Fetal movements Other. Features of a CTG. Baseline Fetal Heart Rate. 110 to 150 bpm at term Faster in early pregnancy

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Understanding Cardiotocography – “CTGs”

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  1. Understanding Cardiotocography – “CTGs”

  2. A Normal Antenatal CTG

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

  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

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

  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 • Up to 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. 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

  13. 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

  14. 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

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