CTG Flashcards
What is CTG?
• Cardiotocography (CTG) is used during pregnancy to monitor fetal heart rate and uterine contractions.
When is a CTG most commonly used?
• It is most commonly used in the third trimester and its purpose is to monitor fetal well-being and allow early detection of fetal distress.
What does an abnormal CTG indicate?
• An abnormal CTG may indicate the need for further investigations and potential intervention.
How does a CTG work?
- The device used in cardiotocography is known as a cardiotocograph. It involves the placement of two transducers onto the abdomen of a pregnant woman.
- One transducer records the fetal heart rate using ultrasound and the other transducer monitors the contractions of the uterus by measuring the tension of the maternal abdominal wall (providing an indirect indication of intrauterine pressure).
- The CTG is then assessed by a midwife and the obstetric medical team.
How should you interpret a CTG?
DR: Define risk C: Contractions BRa: Baseline rate V: Variability A: Accelerations D: Decelerations O: Overall impression
How should you define the risk in a CTG?
o When performing CTG interpretation, you first need to determine if the pregnancy is high or low risk.
o This is important as it gives more context to the CTG reading (e.g. if the pregnancy categorised as high-risk, the threshold for intervention may be lower).
How should you assess contractions?
o Next, you need to record the number of contractions present in a 10 minute period.
o Each big square on the example CTG chart below is equal to one minute, so look at how many contractions occurred within 10 big squares.
o Individual contractions are seen as peaks on the part of the CTG monitoring uterine activity.
o Assess contractions for the following:
o Duration: How long do the contractions last?
o Intensity: How strong are the contractions (assessed using palpation)?
How do you assess the baseline rate of the fatal heart?
o The baseline rate is the average heart rate of the foetus within a 10-minute window.
o Look at the CTG and assess what the average heart rate has been over the last 10 minutes, ignoring any accelerations or decelerations.
o A normal fetal heart rate is between 110-160 bpm.
o Fetal tachycardia is defined as a baseline heart rate greater than 160 bpm.
o Fetal bradycardia is defined as a baseline heart rate of less than 100 bpm.
Causes of fatal tachycardia
Fetal hypoxia Chorioamnionitis Hyperthyroidism Fetal or maternal anaemia Fetal tachyarrhythmia
Causes of fatal bradycardia
o It is common to have a baseline heart rate of between 100-120 bpm in the following situations:
- Postdate gestation
- Occiput posterior or transverse presentations
What is severe prolonged bradycardia?
o Severe prolonged bradycardia (less than 80 bpm for more than 3 minutes) indicates severe hypoxia.
Causes of prolonged severe bradycardia
- Prolonged cord compression
- Cord prolapse
- Epidural and spinal anaesthesia
- Maternal seizures
- Rapid fetal descent
How should you assess variability on a CTG?
o Baseline variability refers to the variation of fetal heart rate from one beat to the next.
o Variability occurs as a result of the interaction between the nervous system, chemoreceptors, baroreceptors and cardiac responsiveness.
o It is, therefore, a good indicator of how healthy a foetus is at that particular moment in time, as a healthy foetus will constantly be adapting its heart rate in response to changes in its environment.
- Should be more than five beats
How should you assess accelerations on a CTG?
o Accelerations are an abrupt increase in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.¹
o The presence of accelerations is reassuring.
o Accelerations occurring alongside uterine contractions is a sign of a healthy foetus.
o The absence of accelerations with an otherwise normal CTG is of uncertain significance.
How should you assess decelerations on a CTG?
o Decelerations are an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.
o The fetal heart rate is controlled by the autonomic and somatic nervous system. In response to hypoxic stress, the foetus reduces its heart rate to preserve myocardial oxygenation and perfusion. Unlike an adult, a foetus cannot increase its respiration depth and rate. This reduction in heart rate to reduce myocardial demand is referred to as a deceleration.
o There are a number of different types of decelerations, each with varying significance.
o Early deceleration, variable deceleration, late deceleration, prolonged deceleration.
