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How to read a CTG

Discussion in 'Gynaecology and Obstetrics' started by Egyptian Doctor, Mar 6, 2014.

  1. Egyptian Doctor

    Egyptian Doctor Moderator Verified Doctor

    Mar 21, 2011
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    What is Cardiotocography?
    Cardiotocography (CTG) is used in pregnancy to monitor both the foetal heart as well as the contractions of the uterus. It is usually only used in the 3rd trimester. It’s purpose is to monitor foetal well-being & allow early detection of foetal distress. An abnormal CTG indicates the need for more invasive investigations & ultimately may lead to emergency caesarian section.

    How it works
    The device used in cardiotocography is known as a cardiotocograph.

    It involves the placement of transducers on the abdomen of a pregnant women.

    One transducer records the foetal heart rate using ultrasound.

    The other transducer monitors the contractions of the uterus.

    It does this by measuring the tension of the maternal abdominal wall.

    This provides an indirect indication of intrauterine pressure.

    The CTG is then assessed by the midwife & obstetric medical team.

    How to read a CTG
    To interpret a CTG you need a structured method of assessing it’s various characteristics.

    The most popular structure can be remembered using the acronym DR C BRAVADO

    DR – Define Risk
    C – Contractions
    BRa – Baseline Rate

    V – Variability

    A – Accelerations

    D – Decelerations
    O - Overall impression

    Define risk
    You first need to assess if this pregnancy is high or low risk

    This is important as it gives more context to the CTG reading

    e.g. If the pregnancy is high risk, your threshold for intervening may be lowered

    Reasons a pregnancy may be considered high risk are shown below¹

    Maternal medical illness
    Gestational diabetes


    Obstetric complications
    Multiple gestation
    Post-date gestation
    Previous cesarean section
    Intrauterine growth restriction
    Premature rupture of the membranes
    Congenital malformations
    Oxytocin induction/augmentation of labor


    Other risk factors
    No prenatal care

    Drug abuse

    Record the number of contractions present in a 10 minute period - e.g. 3 in 10

    Each big square is equal to 1 minute, so you look how many contractions occurred in 10 squares

    Individual contractions are seen as peaks on the part of the CTG monitoring uterine activity

    You should assess contractions for the following:

    • Duration – how long do the contractions last?
    • Intensity – how strong are the contractions? (assessed using palpation)
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    In this example there are 2-3 contractions in a 10 minute period - e.g. 3 in 10


    Baseline rate of foetal heart
    The baseline rate is the average heart rate of the foetus in a 10 minute window

    Look at the CTG & assess what the average heart rate has been over the last 10 minutes

    Ignore any Accelerations or Decelerations

    A normal foetal heart rate is between 110-150 bpm

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    Foetal Tachycardia
    Foetal tachycardia is defined as a baseline heart rate greater than 160 bpm

    It can be caused by:¹

    • Foetal hypoxia
    • Chorioamnionitis – if maternal fever also present
    • Hyperthyroidism
    • Foetal or Maternal Anaemia
    • Foetal tachyarrhythmia

    Foetal Bradycardia
    Foetal bradycardia is defined as a baseline heart rate less than 120 bpm.

    Mild bradycardia of between 100-120bpm is common in the following situations:

    • Post-date gestation
    • Occiput posterior or transverse presentations

    Severe prolonged bradycardia (< 80 bpm for > 3 minutes) indicates severe hypoxia

    Causes of prolonged severe bradycardia are:¹

    • Prolonged cord compression
    • Cord prolapse
    • Epidural & Spinal Anaesthesia
    • Maternal seizures
    • Rapid foetal descent

    If the cause cannot be identified and corrected, immediate delivery is recommended

    Baseline variability refers to the variation of foetal heart rate from one beat to the next

    Variability occurs as a result of the interaction between the nervous system, chemoreceptors, barorecptors & cardiac responsiveness.

    Therefore it is a good indicator of how healthy the foetus is at that moment in time.

    This is because a healthy foetus will constantly be adapting it’s heart rate to respond to changes in it’s environment.


    Normal variability is between 10-25 bpm

    To calculate variability you look at how much the peaks & troughs of the heart rate deviate from the baseline rate (in bpm)


    Variability can be categorised as: 4

    • 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
    • Drugs – opiates, benzodiazipine’s, methyldopa, magnesium sulphate
    • Prematurity – variability is reduced at earlier gestation (<28 weeks)
    • Congenital heart abnormalities

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    Accelerations are an abrupt increase in baseline heart rate of >15 bpm for >15 seconds

    The presence of accelerations is reassuring

    Antenatally there should be at least accelerations every 15 minutes¹

    Accelerations occurring alongside uterine contractions is a sign of a healthy foetus

    However the absence of accelerations with an otherwise normal CTG is of uncertain significance

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    Decelerations are an abrupt decrease in baseline heart rate of >15 bpm for >15 seconds

    There are a number of different types of decelerations, each with varying significance


    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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    Variable deceleration
    Variable decelerations are seen as a rapid fall in baseline rate with a variable recovery phase

    They are variable in their duration & may not have any relationship to uterine contractions

    They are most often seen during labour & in patients with reduced amniotic fluid volume

    Variable decelerations are usually caused by umbilical cord compression¹

    • The umbilical vein is often occluded first causing an acceleration in response
    • Then the umbilical artery is occluded causing a subsequent rapid deceleration
    • When pressure on the cord is reduced another acceleration occurs & then the baseline rate returns
    • Accelerations before & after a variable deceleration are known as the “shoulders of deceleration”
    • There presence indicates the foetus is not yet hypoxic & is adapting to the reduced blood flow.
    Variable decelerations can sometimes resolve if the mother changes position

    The presence of persistent variable decelerations indicates the need for close monitoring

    Variable decelerations without the shoulders is more worrying as it suggests the foetus is hypoxic



    Late deceleration
    Late decelerations begin at the peak of uterine contraction & recover after the contraction ends.

    This type of deceleration indicates there is insufficient blood flow through the uterus & placenta

    As a result blood flow to the foetus is significantly reduced causing foetal hypoxia & acidosis


    Reduced utero-placental blood flow can be caused by: ¹

    • Maternal hypotension
    • Pre-eclampsia
    • Uterine hyper-stimulation

    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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    Prolonged deceleration
    A deceleration that last more than 2 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 quickly – e.g. Foetal blood sampling / emergency C-section


    Sinusoidal Pattern
    This type of pattern is rare, however if present it is very serious

    It is associated with high rates of foetal morbidity & mortality


    It is described as:

    • A smooth, regular, wave-like pattern
    • Frequency of around 2-5 cycles a minute
    • Stable baseline rate around 120-160 bpm
    • No beat to beat variability

    A sinusoidal pattern indicates:

    • Severe foetal hypoxia
    • Severe foetal anaemia
    • Foetal/Maternal Haemorrhage

    Immediate C-section is indicated for this kind of pattern.

    Outcome is usually poor


    Overall impression
    Once you have assessed all aspects of the CTG you need to give your overall impression

    The overall impression can be described as either:

    • Reassuring
    • Suspicious
    • Pathological
    The overall impression is determined by how many of the CTG features were either reassuring, non-reassuring or abnormal. The NICE guideline below demonstrates how to decide which category a CTG falls into.4





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