What is cardiotocography?
Cardiotocography (CTG) is used during pregnancy to monitor fetal heart rate and uterine contractions. 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. An abnormal CTG may indicate the need for further investigations and potential intervention.
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How CTG works
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 uterusby 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 to read a CTG
To interpret a CTG you need a structured method of assessing its 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
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When performing CTG interpretation, you first need to determine if the pregnancy is high or low risk. 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). Some reasons a pregnancy may be considered high risk are shown below.1
Maternal medical illness
- Gestational diabetes
- Multiple gestation
- Previous cesarean section
- Intrauterine growth restriction
- Premature rupture of membranes
- Congenital malformations
- Oxytocin induction/augmentation of labour
Other risk factors
- Absenceof prenatal care
- Drug abuse
Next, you need to record the number of contractions present in a 10 minute period.
Each big square on the example CTG chart below is equal toone minute, so look at how many contractionsoccurred within10 big squares.
Individual contractions are seen as peaks on the part of the CTG monitoring uterine activity.
Assess contractions for the following:
- Duration: How long do the contractions last?
- Intensity: How strong are the contractions (assessed using palpation)?
- In the below example, there are 2 contractions in a 10 minute period (this is often referred to as “2 in 10”).
Baseline rate of the fetal heart
The baseline rate is the average heart rate of the fetus withina 10-minute window.
Look at the CTG and assess what the average heart rate has been over the last 10 minutes, ignoringany accelerations or decelerations.
A normal fetal heart rate is between 110-160 bpm.
Fetal tachycardia is defined as a baseline heart rate greater than 160 bpm.
Causes of fetal tachycardia include:
- Fetal hypoxia
- Fetal or maternal anaemia
- Fetal tachyarrhythmia
Fetal bradycardia is defined as a baseline heart rate of less than 110 bpm.
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
Severe prolonged bradycardia (less than 80 bpm for more than 3 minutes) indicates severe hypoxia.
Causes of prolonged severe bradycardia include:
- Prolonged cord compression
- Cord prolapse
- Epidural andspinal anaesthesia
- Maternal seizures
- Rapid fetal descent
Baseline variability refers to the variation of fetal heart rate from one beat to the next.
Variability occurs as a result of the interaction between the nervous system, chemoreceptors, baroreceptors and cardiac responsiveness.
It is, therefore, a good indicator of how healthy a fetus is at that particular moment in time, as a healthy fetus will constantly be adapting its heart rate in response to changes in its environment.
Normal variability indicates an intact neurological system in the fetus.
Normal variability is between 5-25 bpm.3
To calculate variability you need to assess how much the peaks and troughs of the heart rate deviate from the baseline rate (in bpm).
Variability can be categorised as either reassuring, non-reassuring or abnormal. 3
Reassuring: 5 – 25 bpm
- less than 5 bpm for between 30-50 minutes
- more than 25 bpm for 15-25 minutes
- less than 5 bpm for more than 50 minutes
- more than 25 bpm for more than 25 minutes
Reduced variability can be caused by any of the following:2
- Fetal sleeping: this should last no longer than 40 minutes (this is the most common cause)
- Fetal acidosis (due to hypoxia): more likely if late decelerations are also present
- Fetal tachycardia
- Drugs: opiates, benzodiazepines, methyldopa and magnesium sulphate
- Prematurity: variability is reduced at earlier gestation (<28 weeks)
- Congenital heart abnormalities
Accelerations are an abrupt increase in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.1
The presence of accelerations is reassuring.
Accelerations occurring alongside uterine contractions is a sign of a healthy fetus.
The absence of accelerations with an otherwise normal CTG is of uncertain significance.
Decelerations are an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.
The fetal heart rate is controlled by the autonomic and somatic nervous system. In response to hypoxic stress, the fetus reduces its heart rate to preserve myocardial oxygenation and perfusion. Unlike an adult, a fetus cannot increase its respiration depth and rate. This reduction in heart rate to reduce myocardial demand is referred to as a deceleration.
There are a number of different types of decelerations, each with varying significance.
Early decelerations start when the uterine contraction begins and 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 and intracranial pressure reduces. This type of deceleration is, therefore, considered to be physiological and not pathological.3
Variable decelerations are observedas a rapid fall in baseline fetal heart rate with a variable recovery phase.
They are variable in their duration and may not have any relationship to uterine contractions.
They are most often seen during labour and in patients’ with reduced amniotic fluid volume.
All fetusesexperience stress during the labour process, as a result of uterine contractions reducing fetal perfusion. Whilst fetal stress is to be expected during labour, the challenge is to pick up pathological fetaldistress.
Variable decelerations are usually caused by umbilical cord compression. The mechanism is as follows:1
1. The umbilical vein is often occluded first causing an acceleration of the fetal heart rate in response.
2. Then the umbilical artery is occluded causing a subsequent rapid deceleration.
3. When pressure on the cord is reduced another acceleration occurs and then the baseline rate returns.
The accelerations before and after a variable deceleration are known as the shoulders of deceleration. Their presence indicates the fetus is not yet hypoxic and 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 are more worrying, as it suggests the fetus is becoming hypoxic.
Late decelerations begin at the peak of the uterine contraction and recover after the contraction ends. This type of deceleration indicates there is insufficient blood flow to the uterus and placenta. As a result, blood flow to the fetus is significantly reduced causing fetal hypoxia and acidosis.
Causes of reduced uteroplacental blood flow include:1
- Maternal hypotension
- Uterine hyperstimulation
A prolonged deceleration is defined as a deceleration that lasts 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.
A sinusoidal CTG pattern is rare, however, if present it is very concerning as it is associated with high rates of fetal morbidity and mortality.1
A sinusoidal CTG pattern has the following characteristics:
- A smooth, regular, wave-like pattern
- Frequency of around 2-5 cycles a minute
- Stable baseline rate around 120-160bpm
- No beat to beat variability
A sinusoidal pattern usually indicates one or more of the following:
- Severe fetal hypoxia
- Severe fetal anaemia
- Fetal/maternal haemorrhage
Once you have assessed all aspects of the CTG you need to determine your overall impression.
The overall impression can be described as either reassuring, suspicious or abnormal.3
Overall impression is determined by how many of the CTG features were either reassuring, non-reassuring or abnormal. The NICE guidelines below demonstrate how to decide which category a CTG falls into.3
Baseline heart rate
- 110 to 160 bpm
- 5 to 25 bpm
- None or early
- Variable decelerations with no concerning characteristics for less than 90 minutes
Baseline heart rate
Either of the below would be classed as non-reassuring:
- 100 to 109 bpm
- 161 to 180 bpm
Either of the below would be classed as non-reassuring:
- Less than 5 for 30 to 50 minutes
- More than 25 for 15 to 25 minutes
Any of the below would be classed as non-reassuring:
- Variable decelerations with no concerning characteristics for 90 minutes or more.
- Variable decelerations with any concerning characteristics in up to 50% of contractions for 30 minutes or more.
- Variable decelerations with any concerning characteristics in over 50% of contractions for less than 30 minutes.
- Late decelerations in over 50% of contractions for less than 30 minutes, with no maternal or fetal clinical risk factors such as vaginal bleeding or significant meconium.
Baseline heart rate
Either of the below would be classed as abnormal:
- Below 100 bpm
- Above 180 bpm
Any of the below would be classed as abnormal:
- Less than 5 for more than 50 minutes
- More than 25 for more than 25 minutes
Any of the below would be classed as abnormal:
- Variable decelerations with any concerning characteristics in over 50% of contractions for 30 minutes (or less if any maternal or fetal clinical risk factors – see above).
- Late decelerations for 30 minutes (or less if any maternal or fetal clinical risk factors).
- Acute bradycardia, or a single prolonged deceleration lasting 3 minutes or more.
Regard the following as concerning characteristics of variable decelerations:
- Lasting more than 60 seconds
- Reduced baseline variability within the deceleration
- Failure to return to baseline
- Biphasic (W) shape
- No shouldering
Dr Venkatesh Subramanian
Obstetrics & Gynaecology Registrar in London
- AMIR SWEHA, M.D.Interpretation of the Electronic Fetal Heart Rate During Labor. Am Fam Physician. 1999 May 1;59(9):2487-2500. Available from: [LINK].
- Clinical obstetrics and gynaecology. 2nd Edition. 2009. B.Magowan, Philip Owen, James Drife.
- Intrapartum care: NICE guideline CG190 (February 2017). Available from: [LINK].
What is a good CTG reading? ›
Normal antenatal CTG trace: The normal antenatal CTG is associated with a low probability of fetal compromise and has the following features: Baseline fetal heart rate (FHR) is between 110-160 bpm • Variability of FHR is between 5-25 bpm • Decelerations are absent or early • Accelerations x2 within 20 minutes.How do you read a contraction monitor paper? ›
When you're looking at the screen, the fetal heart rate is usually on the top and the contractions at the bottom. When the machine prints out graph paper, you'll see the fetal heart rate to the left and the contractions to the right. Sometimes it's easier to read printouts by looking at them sideways.What is a strong contraction number? ›
Braxton Hicks contractions. Varies between 5-25 mmHg. Active labor contractions. Intensity of a contraction is between 40-60 mmHg.What is considered a contraction 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.Which CTG findings indicate fetal distress? ›
Signs of fetal distress may include decelerations occurring after uterine contractions (late decelerations), variable decelerations, and beat‐to‐beat variability noted on the tracing.What are normal contraction numbers? ›
Contractions can be described by frequency, duration, strength (amplitude), uniformity, and shape. During normal labor, the amplitude of contractions increases from an average of 30 mm Hg in early labor to 50 mm Hg in later first stage and 50 to 80 mm Hg during the second stage.What is dominant peak on CTG? ›
It can be found that the dominant peak occurs at the cycle frequency of 2.35 Hz; that is, the FHR of this segment is bpm. Figure 1(c) shows the heavy noise part of the signal. The signal is so heavily contaminated by noises that the heart beats cannot be identified by human visual inspection.What is an abnormal CTG? ›
An abnormal CTG has two or more features which are non-reassuring, or any abnormal features. Further information about classifying FHR traces: If repeated accelerations are present with reduced variability, the FHR trace should be regarded as reassuring.What do the lines on a contraction monitor mean? ›
What do the lines on the EFM mean? The top line shows the baby's heartbeat. Certain patterns can show how your baby is handling labor. The bottom line shows your contractions. Comparing your baby's heartbeat with your contractions shows how your baby is handling the labor.What does Toco mean on a CTG? ›
Cardiotocography (CTG) is a technical means of recording (-graphy) the fetal heartbeat (cardio-) and the uterine contractions (-toco-) during pregnancy, typically in the third trimester. The machine used to perform the monitoring is called a cardiotocograph, more commonly known as an electronic fetal monitor.
How do you know when contractions are strong enough? ›
Your contractions are regular. Your contractions are about five to 10 minutes apart or less, and they've been going on for an hour. The pain in your belly or lower back doesn't go away when you move or change positions. You have a bloody (brownish or reddish) mucus discharge.How do I know my contraction strength? ›
The intensity of the contractions can be estimated by touching the uterus. The relaxed or mildly contracted uterus usually feels about as firm as a cheek, a moderately contracted uterus feels as firm as the end of the nose, and a strongly contracted uterus is as firm as the forehead.What is a good contraction pattern? ›
In a normal labor, one contraction every two to three minutes or less than five contractions in a 10 minute period is ideal. A uterus must rest between contractions, having sufficient uterine resting tone (soft to the touch), and uterine resting time (about one minute).What numbers show contractions? ›
The intensity of Braxton Hicks contractions varies between approximately 5-25 mm Hg (a measure of pressure). For comparison, during true labor the intensity of a contraction is between 40-60 mm Hg in the beginning of the active phase.Whats the rule of thumb for contractions? ›
Other ways to recognize labor:
The 5-1-1 Rule: The contractions come every 5 minutes, lasting 1 minute each, for at least 1 hour. Fluids and other signs: You might notice amniotic fluid from the sac that holds the baby.
The relation between fetal distress and the subsequent condition at birth was studied in 2791 pregnancies. Fetal distress was defined as a heart rate greater than 160 or less than 120/min between uterine contractions, with or without meconium-stained liquor.What are the 4 types of fetal heart decelerations? ›
Decelerations are temporary drops in the fetal heart rate. There are three basic types of decelerations: early decelerations, late decelerations, and variable decelerations. Early decelerations are generally normal and not concerning. Late and variable decelerations can sometimes be a sign the baby isn't doing well.How can you tell if a fetus is in distress? ›
A low heart rate, or unusual patterns in the heart rate, could signal fetal distress. Checking the fetal heart rate is a good way to find out if it's tolerating pregnancy and labor well. During pregnancy your obstetrician may recommend other tests to monitor the fetal heart rate: Nonstress test.What number is considered active labor? ›
Active labor. During active labor, your cervix will dilate from 6 centimeters (cm) to 10 cm. Your contractions will become stronger, closer together and regular.How many contractions is considered active labor? ›
What is active labor? During active labor, your cervix dilates to about 7 to 8 centimeters. Contractions will be more evenly spaced, intense, and frequent, coming about every three to four minutes apart. Active labor usually lasts from two to three-and-a-half hours (with a wide range of what's considered normal).
What is good fetal variability? ›
The normal FHR tracing include baseline rate between 110-160 beats per minute (bpm), moderate variability (6-25 bpm), presence of accelerations and no decelerations.What are abnormal fetal heart tones? ›
Fetal Arrhythmia/Dysrhythmia. A healthy fetus has a heartbeat of 120 to 160 beats per minute, beating at a regular rhythm. Arrhythmia most often refers to an irregular heartbeat, while dysrhythmia represents all types of abnormal heartbeats: the heartbeat can be too fast (tachycardia) or too slow (bradycardia).What is overshooting on a CTG? ›
Fetal heart rate “overshoots” occur immediately following the peak of the underlying uterine contraction (Figure 5), as the fetus attempts to normalise the blood pressure by abruptly increasing the heart rate to compensate for ongoing, transient hypotension as a result of sustained and total compression of the ...What causes decelerations on CTG? ›
They are caused by decreased blood flow to the placenta and can signify an impending fetal acidemia. Typically, late decelerations are shallow, with slow onset and gradual return to normal baseline. The usual cause of the late deceleration is uteroplacental insufficiency.What does acute hypoxia look like on a CTG? ›
Acute hypoxia presents as a prolonged deceleration lasting for more than 5 minutes or for more than 3 minutes if associated with reduced variability within the deceleration. Fetal pH drops at a rate of 0.01/min during the deceleration (Gull et al 1996).Are variable decelerations normal? ›
Finally, variable decelerations are the most common type of fetal deceleration. They typically occur during the first and second stages of labor (i.e., the initial contractions and dilation of the cervix leading to the delivery of the infant, respectively) and vary in shape, duration, and intensity.What should baby's heart rate be on CTG? ›
CTG: electronic fetal monitoring machine
It is normal for a baby's heart rate to vary between 110 and 160 beats a minute. This is much faster than your own heart rate, which is about 60-100 beats per minute. A heart rate in your baby that doesn't vary or is too low or too high may mean that there is a problem.
The purpose of CTG recordings is to identify when there is concern about fetal well-being to allow interventions to be carried out before the fetus is harmed. The focus is on identifying fetal heart rate (FHR) patterns associated with inadequate oxygen supply to the fetus.