Cardiotocography (CTG)

Question 1

What is cardiotocography?

Answer 1

Cardiotocography (CTG) is used to measure the fetal heart rate and the contractions of the uterus. It is also known as electronic fetal monitoring. It is a useful way of monitoring the condition of the fetus and the activity of labour.

CTG can help guide decision making and delivery. However, it should not be used in isolation for decision making, and it is essential to take into account the overall clinical picture.

Question 2

How is the CTG operated?

Answer 2

Two transducers are placed on the abdomen to get the CTG readout:

One above the fetal heart to monitor the fetal heartbeat

One near the fundus of the uterus to monitor the uterine contractions

Question 3

Indications for CTG in labour?

Answer 3

The indications for continuous CTG monitoring in labour include:

Sepsis
Maternal tachycardia (> 120)
Significant meconium
Pre-eclampsia (particularly blood pressure > 160 / 110)
Fresh antepartum haemorrhage
Delay in labour
Use of oxytocin
Disproportionate maternal pain

Question 4

What features should be looked for on a CTG?

Answer 4

There are five key features to look for on a CTG:

Contractions – the number of uterine contractions per 10 minutes
Baseline rate – the baseline fetal heart rate
Variability – how the fetal heart rate varies up and down around the baseline
Accelerations – periods where the fetal heart rate spikes
Decelerations – periods where the fetal heart rate drops

Question 5

Contractions CTG?

Answer 5

Contractions are used to gauge the activity of labour. Too few contractions indicate labour is not progressing. Too many contractions can mean uterine hyperstimulation, which can lead to fetal compromise. It is also important to interpret the fetal heart rate in the context of the uterine contractions.

Question 6

Accelerations CTG?

Answer 6

Accelerations are generally a good sign that the fetus is healthy, particularly when occurring alongside contractions of the uterus.

Question 7

Baseline rate and variability CTG?

Answer 7

Question 8

Decelerations CTG?

Answer 8

Decelerations are a more concerning finding. The fetal heart rate drops in response to hypoxia. The fetal heart rate is slowing to conserve oxygen for the vital organs. There are four types of decelerations to be aware of:

Early decelerations
Late decelerations
Variable decelerations
Prolonged decelerations

Question 9

What are early decelerations?

Answer 9

Early decelerations are gradual dips and recoveries in heart rate that correspond with uterine contractions. The lowest point of the declaration corresponds to the peak of the contraction. Early decelerations are normal and not considered pathological. They are caused by the uterus compressing the head the fetus, stimulating the vagus nerve of the fetus, slowing the heart rate.

Question 10

What are late decelerations?

Answer 10

Late decelerations are gradual falls in heart rate that starts after the uterine contraction has already begun. There is a delay between the uterine contraction and the deceleration. The lowest point of the declaration occurs after the peak of the contraction. Late decelerations are caused by hypoxia in the fetus, and are a more concerning finding. They may be caused by excessive uterine contractions, maternal hypotension or maternal hypoxia.

Question 11

What are variable decelerations?

Answer 11

Variable decelerations are abrupt decelerations that may be unrelated to uterine contractions. There is a fall of more than 15 bpm from the baseline. The lowest point of the deceleration occurs within 30 seconds, and the deceleration lasts less than 2 minutes in total. Variable decelerations often indicate intermittent compression of the umbilical cord, causing fetal hypoxia. Brief accelerations before and after the deceleration are known as shoulders, and are a reassuring sign that the fetus is coping.

Question 12

Prolonged deceleration?

Answer 12

Prolonged decelerations last between 2 and 10 minutes with a drop of more than 15 bpm from baseline. This often indicates compression of the umbilical cord, causing fetal hypoxia. These are abnormal and concerning.

Question 13

4 categories for CTG?

Answer 13

The NICE guidelines (2017) recommend categorising the CTG based on three features of the CTG described above:

Baseline rate
Variability
Decelerations

Normal
Suspicious: a single non-reassuring feature
Pathological: two non-reassuring features or a single abnormal feature
Need for urgent intervention: acute bradycardia or prolonged deceleration of more than 3 minutes

Question 14

Foetal bradycardia rule of 3’s?

Answer 14

There is a “rule of 3’s” for fetal bradycardia when they are prolonged:

3 minutes – call for help
6 minutes – move to theatre
9 minutes – prepare for delivery
12 minutes – deliver the baby (by 15 minutes)

Question 15

Sinusoidal CTG?

Answer 15

A sinusoidal CTG is a rare pattern to be aware of, as it can indicate severe fetal compromise. It gives a pattern similar to a sine wave, with smooth regular waves up and down that have an amplitude of 5 – 15 bpm. It is usually associated with severe fetal anaemia, for example, caused by vasa praevia with fetal haemorrhage.

Question 16

Mnemonic to assess features of a CTG?

Answer 16

DR C BRaVADO is a mnemonic often taught to assess the features of a CTG in a structured way. It involves assessing in order:

DR – Define Risk (define the risk based on the individual woman and pregnancy before assessing the CTG)
C – Contractions
BRa – Baseline Rate
V – Variability
A – Accelerations
D – Decelerations
O – Overall impression (given an overall impression of the CTG and clinical picture)

If you are asked to assess a CTG in your exams, use the DR C BRaVADO structure to describe each feature in turn. Give an overall impression of the CTG as being normal (all features are reassuring), suspicious, pathological, or need for urgent intervention, as described in the NICE guidelines (2017).