Post Course Notes in Obstetrics by Shabnam Bobdiwala
Cardiotocography: an introduction
CTG stands for cardiotocography. It is a way to monitor the fetal heart rate and maternal uterine
contractions in the late second and third trimesters of pregnancy.
A CTG can either be:
•
•
•
Normal
Non-reassuring
Abnormal
There are several features that are assessed to determine which category a CTG fits into:
The mnemonic ‘DR C BRAVADO’ is often used.
DR = define risk
C = contractions
BRA = baseline rate
V = variability
A = accelerations
D = decelerations
O = overall impression
Define risks: this will influence how you interpret your CTG. Risks include pre-eclampsia,
gestational diabetes, a preterm fetus, etc. The greater the number of risk factors, the more
cautiously a CTG is likely to be interpreted.
Contractions: these are at the bottom of the CTG. One aims for four contractions every 10
minutes in labour (also denoted as 4:10). Note that factors which may irritate the uterus such as a
placental abruption or a urinary tract infection may mimic uterine activity although this does not tend
to be as intermittent as contractions associated with labour.
Example showing regular contractions:
Contractions
© Dr R Clarke
www.askdoctorclarke.com
1
Post Course Notes in Obstetrics by Shabnam Bobdiwala
Example showing no contractions:
Baseline rate: this is the baseline heart rate of the fetus. It is normally 110-160bpm in a term (37
weeks gestation or more) fetus. A preterm fetus may have a higher baseline rate.
The baseline rate here is 130bpm
Baseline
Rate 130
© Dr R Clarke
www.askdoctorclarke.com
2
Post Course Notes in Obstetrics by Shabnam Bobdiwala
Variability:
This term relates to fluctuations in the baseline rate. A normal variability is >5 beats either side of
the baseline. Variability of 0-5 beats is termed reduced variability. This is a cause for concern if it
persists for more than 90 minutes. Shorter periods of reduced variability are normal as the fetus
undergoes a ‘sleep-wake cycle’, where the variability is physiologically reduced when the fetus is
asleep and the CTG is accelerative when the fetus is awake.
Example of sleep wake cycle:
Asleep
Awake
Reduced variability:
+/- 3bpm
© Dr R Clarke
www.askdoctorclarke.com
3
Post Course Notes in Obstetrics by Shabnam Bobdiwala
Accelerations:
‘An abrupt rise of >15 beats in the baseline lasting for at least 15 seconds’.
This indicates fetal activity and the presence of accelerations indicates fetal wellbeing.
Accelerations
Decelerations: ‘an abrupt drop of >15 beats in the baseline lasting for at least 15 seconds’
The presence of decelerations may indicate fetal distress. However, the presence of decelerations
does not always warrant intervention. They may resolve by themselves by simple measures such
as a change of maternal position and increasing maternal fluid intake. Decelerations are described
as early, variable or late, relating to the timing of the start of the deceleration in relation to a
contraction.
Early decelerations are uncommon, benign and usually associated with fetal head compression.
Variable decelerations are very common, can be a normal feature in an otherwise uncomplicated
labour and birth, and are usually a result of cord compression.
Late decelerations start after a contraction and often have a slow return to baseline. The longer,
the later and the deeper individual decelerations are, the more likely it is that there will be fetal
acidosis. Here is an example of a late deceleration, starting soon after a contraction
Example of single late deceleration
Single deceleration
© Dr R Clarke
www.askdoctorclarke.com
4
Post Course Notes in Obstetrics by Shabnam Bobdiwala
Example of variable decelerations
These decelerations are difficult to interpret as the monitoring of contractions is not optimal but they
are likely to be variable (the commonest type of deceleration).
Multiple decelerations
Overall impression:
This is your judgment on whether the CTG is normal, non-reassuring or abnormal.
© Dr R Clarke
www.askdoctorclarke.com
5
Post Course Notes in Obstetrics by Shabnam Bobdiwala
Case study:
This is a 32 year old P0+0 who is at 41+4 weeks, who is being induced for postdates.
She is otherwise fit and well and there have been no concerns about the pregnancy antenatally.
She is given a 10mg Propess vaginal pessary and this is removed 24 hours later.
She then goes to the labour ward for the next stage of her induction of labour.
What do you think of the initial CTG on labour ward?
DR = postdates, induction of labour
C = 1-2:10
BRA = 115
V = >5
A = present
D = absent
O = normal
Q: What do you notice about her contractions?
© Dr R Clarke
www.askdoctorclarke.com
6
Post Course Notes in Obstetrics by Shabnam Bobdiwala
A: They are not regular enough
She therefore undergoes an ARM and is started on an oxytocin hormone drip.
What do you think of her CTG four hours after starting the hormone drip?
DR = postdates, induction of labour
C = 3:10
BRA = 160
V = >5
A = present
D = absent
O = normal (although note the rise in the baseline rate from 130 to 160)
She makes good progress and gets to full dilatation. During the second stage of labour (after 30
minutes of pushing) her CTG looks like this. Report on this CTG
© Dr R Clarke
www.askdoctorclarke.com
7
Post Course Notes in Obstetrics by Shabnam Bobdiwala
DR = postdates, induction of labour
C = 4:10
BRA = difficult to determine
V = >5
A = absent
D = present
O = abnormal
These decelerations are worrying and this fetus needs urgent delivery.
She has a ventouse delivery of a 3.2kg baby born in good condition. Both mother and baby do well.
Important Note
These notes were written by Shabnam Bobdiwala in 2015. They are presented in good faith and every effort has been
taken to ensure their accuracy. Nevertheless, medical practice changes over time and it is always important to check the
information with your clinical teachers and with other reliable sources. Disclaimer: no responsibility can be taken by either
the author or publisher for any loss, damage or injury occasioned to any person acting or refraining from action as a result of
this information.
Please give feedback on this document and report any inaccuracies to:
[email protected]
© Dr R Clarke
www.askdoctorclarke.com
8