CARDIOTOCOGRAPHY

WHAT IS CTG?

• 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.

WORKING OF CTG

• The device used in cardiotocography is known as a cardiotocograph.

• It involves the placement of 2 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 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 RiskC – ContractionsBRa – Baseline RateV – Variability

• A – Accelerations

• D – DecelerationsO - 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 diabetesHypertensionAsthma

Obstetric complications

• Multiple gestationPost-date gestationPrevious cesarean sectionIntrauterine growth restrictionPremature rupture of the membranesCongenital malformationsOxytocin induction/augmentation of laborPre-eclampsia

Other risk factors

• No prenatal careSmoking

• Drug abuse

CONTRACTIONS

• 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)

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 bpm¹

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

VARIABILITY

• 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 bpm³

• 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: ³

• 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

• Accelerations

• 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 2 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

• 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