Cardiotocography (CTG) Interpretation Flashcards
How is fetal monitoring achieved in low risk pregnancies?
- intermittent auscultation to listen to the fetal heart
- this is acheived through Doppler
How is fetal monitoring acheived in high risk pregnancies?
continuous monitoring with CTG
What features may make a pregnancy become “high risk” and require CTG monitoring?
- intrauterine growth restriction (IUGR)
- multiple pregnancy
- meconium stained liquor
- oxytocin infusion
- abnormality on intermittent auscultation
meconium staining can be normal post 40 weeks gestation but is a sign of distress prior to this
What is measured on CTG?
- fetal heart rate
- contractions of the uterus
What are arrows A-D pointing at?
A - fetal heart rate in bpm
B - fetal movements (mother presses button when she feels movement)
C - fetal movements (detected by the computer)
D - uterine contractions
What is a fetal scalp electrode?
an instrument that screws into the scalp to monitor the fetal HR
When is a fetal scalp electrode used?
- obesity
- twins
- abdominal scarring
- poor quality trace with abdominal transducer
it should be AVOIDED in blood-borne viruses / haemophilia
What are the indications for continuous CTG monitoring in labour?
- sepsis
- maternal tachycardia (>120)
- significant meconium
- pre-eclampsia
- fresh antepartum haemorrhage
- delay in labour
- oxytocin use
- disproportionate maternal pain
What are the 5 components of the CTG?
contractions:
- the number of uterine contractions per 10 mins
baseline rate:
- baseline fetal HR
variability:
- how the fetal HR varies up and down around the baseline
accelerations:
- periods where the fetal HR spikes
decelerations:
- periods where the fetal HR drops
What is the normal rate for contractions?
4 or 5 contractions should occur every 10 mins whilst in labour
Why is it important to interpret uterine contractions?
- contractions are used to gauge the actvity of labour
- too few contractions indicates that labour is not progressing
- too many contractions indicates uterine hyperstimulation + risk of fetal compromise
What is a normal baseline rate?
110 - 160 bpm
What is a normal value for variability?
5 bpm or more
How can baseline rate and variability be described?
- reassuring
- non-reassuring
- abnormal
What is a reassuring baseline rate / variability?
baseline rate:
- between 110 - 160 bpm
variability:
- between 5 - 25
What is a non-reassuring baseline rate / variability?
baseline rate:
- 100 - 109 bpm
OR
- 161 - 180 bpm
variability:
- < 5 for 30-50 mins
OR
- > 25 for 15-25 mins
What is an abnormal baseline rate / variability?
baseline rate:
- below 100 or above 180
variability:
- < 5 for over 50 mins
OR
- > 25 for more than 25 mins
What is an acceleration?
- a rise of > 15bpm for 15 seconds
- accelerations occurring alongside uterine contractions is a sign of a healthy fetus
the absence of accelerations with an otherwise normal CTG is not necessarily a concerning sign
What is a deceleration?
- a fall of > 15 bpm for > 15 seconds
- this is a sign of fetal distress
What aspects of uterine contractions are assessed?
- count how many contractions occur in 10 mins (each square = 1 min)
- assess duration of the contractions
- assess intensity by palpating the abdomen
the CTG does NOT give any indication of contraction intensity
this must be gauged by palpating the abdomen
How is the baseline rate calculated?
- look at the CTG and assess what the average heart rate has been over the last 10 mins
- ignore any accelerations or decelerations
How is variability calculated?
- by assessing how much the peaks / troughs of the HR deviate from the baseline rate
Why are decelerations a concerning sign?
- the fetal HR drops in response to hypoxia
- it is slowing down to conserve energy for vital organs
What are the 4 types of deceleration?
- early decelerations
- late decelerations
- variable decelerations
- prolonged decelerations
What are early decelerations?
- early decelerations are related to uterine contractions
- they start when the contraction begins and recover when the contraction stops
What causes an early deceleration?
- the uterus compresses the fetal head, which stimulates the vagus nerve and slows the HR
- this is NOT pathological
What is a late deceleration?
late decelerations begin at the peak of uterine contraction and recover when the contraction ends
What causes a late deceleration?
insufficient blood flow to the uterus + placenta due to:
- maternal hypotension
- pre-eclampsia
- uterine hyperstimulation
this can result in fetal hypoxia + acidosis
What are variable decelerations?
- a rapid fall in baseline fetal HR with a variable recovery phase
- their duration is variable and they do NOT have a relationship to uterine contractions
Describe the course of a variable deceleration
- there is a fall of > 15 bpm from the baseline
- the lowest point of the deceleration occurs within 30 seconds
- the deceleration lasts for < 2 mins in total
How are variable decelerations described?
in terms of depth and duration
What do variable accelerations indicate?
- intermittent compression of the umbilical cord, causing fetal hypoxia
- they are normally seen during labour + in women with reduced amniotic fluid volume
What are the shoulders of deceleration?
- accelerations that occur before and after a variable decleration
- their presence indicates the fetus is not yet hypoxic + is adapting to redcued blood flow
What is a prolonged deceleration?
a decleration that lasts for more than 2 minutes
When is a CTG described as reassuring in terms of decelerations?
- there are no declerations
- there are early decelerations
- there are < 90 seconds of variable decelerations with no concerning features
What features of decelerations can make then non-reassuring or abnormal?
- regular variable decelerations / late decelerations can be abnormal or non-reassuring depending on their features
- prolonged decelerations are always abnormal
How can a CTG be categorised based on baseline rate, declerations + variability?
normal
suspicious:
- a single non-reassuring feature
pathological:
- 2 non-reassuring features
OR
- a single abnormal feature
need for urgent intervention:
- acute bradycardia
OR
- prolonged decleration for > 3 mins
What is the “rule of 3s” for fetal bradycardia?
- 3 mins - call for help
- 6 mins - move to theatre
- 9 mins - prepare for delivery
- 12 mins - delivery of the baby (by 15 mins)
What is a sinusoidal CTG pattern?
- indicates severe fetal compromise
- pattern is similar to a sine wave
- stable baseline rate around 120-160bpm with no beat to beat variability
What can a sinusoidal CTG indicate?
- severe fetal hypoxia
- severe fetal anaemia
- fetal / maternal haemorrhage
What is fetal bradycardia?
When does it become more concerning?
- a baseline HR < 110 bpm
- severe prolonged bradycardia occurs when the HR < 80 for more than 3 mins
What are the causes of prolonged severe bradycardia?
- prolonged cord compression
- cord prolapse
- epidural / spinal anaesthesia
- maternal seizures
- rapid fetal descent
When is it normal to have a baseline rate of 100-120bpm?
- postdate gestation
OR
- occipitoposterior / transverse presentations
What are the possible causes of reduced variability?
- fetal sleeping (should last < 40 mins)
- fetal acidosis (due to hypoxia)
- fetal tachycardia
- drugs
- prematurity (reduced < 28 weeks gestation)
- congenital heart abnormalities
fetal acidosis is more likely if decelerations are also present
What drugs are associated with reduced variability?
- methyldopa
- opiates
- benzodiazepines
- magnesium sulphate
What would you want to do if a CTG was non-reassuring or abnormal?
fetal blood sample
- this assesses for fetal acidosis
- determines the need for emergency LSCS
