CTG

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What is Cardiotocography?

Cardiotocography:(CTG) is used in pregnancy to monitor both the fetal heart as well as the contractions of the uterus. It is usually only used in the 3rd trimester. Its purpose is to monitor fetal well-being & allow early detection of fetal 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 2 transducers on the abdomen of pregnant women. One transducer records the fetal 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 its variouscharacteristics. The most popular structure cans be rememberedusing 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 riskThis isimportant 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
Hypertension
Asthma

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
Pre-eclampsia

Other risk factors

No prenatal care
Smoking

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 manycontractions 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

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Baseline rate of fetal heart

The baseline rate is the average heart rate of the fetus 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 fetal heart rate is between 110-150 bpm¹

Fetal Tachycardia

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

It can be caused by:

§  Fetal hypoxia

§  Chorioamnionitis – if maternal fever also present

§  Hyperthyroidism

§  Fetal or Maternal Anemia

§  Fetal tachyarrhythmia

Fetal Bradycardia

Fetal 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:

§  Prolonged cord compression

§  Cord prolapse

§  Epidural & Spinal Anesthesia

§  Maternal seizures

§  Rapid fetal descent

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

Variability

Baseline variability refers to the variation of fetal heart rate from one beat to the nextVariability occurs as a result of the interaction between the nervous system, chemoreceptors, baroreceptors& cardiac responsiveness. Therefore it is a good indicator of how healthy the fetus is at that moment in time. This is because a healthy fetus will constantly be adapting it’s heart rate to respond to changes in its environment.

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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)

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Variability can be categorized as: 

§  Reassuring – ≥ 5 bpm

§  Non-reassuring – < 5bpm for between 40-90 minutes

§  Abnormal – < 5bpm for >90 minutes

 

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Reduced variability can be caused by: 

§  Fetus sleeping - this should last no longer than 40 minutes – most common cause

§  Fetal acidosis (due to hypoxia) – more likely if late decelerations also present

§  Fetal tachycardia

§  Drugs – opiates, benzodiazepine’s, methyldopa, magnesium sulphate

§  Prematurity – variability is reduced at earlier gestation (<28 weeks)

§  Congenital heart abnormalities

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Accelerations

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

The presence of accelerations is reassuring

Antenatal there should be at least 2 accelerations every 15 minutes¹

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

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

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Early deceleration

Early decelerations start when uterine contraction begins & recover when uterine contraction stops

This is due to increased fetal 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

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 labor& in patients with reduced amniotic fluid volume

Variable decelerations are usually caused by umbilical cord compression

§  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 fetus 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 fetus is hypoxic

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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 fetus is significantly reduced causing fetal hypoxia & acidosis

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Reduced utero-placental blood flow can be caused by:

§  Maternal hypotension

§  Pre-eclampsia

§  Uterine hyper-stimulation

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The presence of late decelerations is taken seriously &fetal blood sampling for pH is indicated

If fetal blood pH is acidotic it indicates significant fetal 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-Reassuring

If it lasts longer than 3 minutes it is immediately classed as Abnormal

Action must be taken quickly – e.g. fetal blood sampling / emergency C-section

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Sinusoidal Pattern

This type of pattern is rare, however if present it is very seriousIt is associated with high rates of fetal morbidity & mortality

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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 fetal hypoxia

§  Severe fetalanemia

§  Fetal/Maternal Hemorrhage

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

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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.