Fetal Monitoring In Labour Flashcards
What device is used?
A cardiotocograph
How is a CTG done?
Placement of 2 transducers onto abdomen
One records fetal heart rate using ultrasound and the other transducer monitors the contractions of the uterus by measuring the tension of the maternal abdominal wall - an indirect indication of intrauterine pressure
What is the acronym used to read a CTG?
DR: define risk C: contractions BRA: baseline rate V: variation ps A: accelerations D: decelerations O: overall impression
What does define risk mean?
The need to determine whether the pregnancy is high or low risk
Gives more context to the CTG
Reasons for high risk:
Maternal medical illness - asthma, HTN, GDM
Obstetric complications - post date, previous CS, IUGR, PROM, congenital malformations, IOL, pre-eclampsia
Others: smoking, drug abuse, absence of prenatal care
What should be assessed with regards to contractions?
The number present in a 10 minute period
Individual contractions = peaks on the part measuring uterine activity
Assess for:
Duration
Intensity - assessed using palpation
What is the baseline rate?
The average HR of the fetus within a 10 min window Normal: 110-160bpm Fetal tachycardia: baseline HR> 160 If >180 = abnormal Fetal bradycardia: baseline <100
What can cause fetal tachycardia?
Fetal hypoxia Chorioamnionitis Hyperthyroidism Fetal or maternal anaemia Fetal tachyarrhythmia
When is it common to have a baseline HR between 100-120?
Post date gestation
Occiput posterior or transverse presentations
What does severe prolonged bradycardia indicate? (Less than 80bpm for more than 3 mins)
Severe hypoxia
What causes of prolonged severe bradycardia are there?
Prolonged cord compression Cord prolapse Epidural and spinal anaesthesia Maternal seizures Rapid fetal descent
What does baseline variability refer to?
The variation of fetal HR 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 an indicator of how healthy fetus is in that moment in time, a healthy fetus will constantly be adapting its HR in repossessed to changes in the environment
Normal variability indicates an intact neurological system in fetus
What is normal variability?
Between 5 and 25bpm
How do you calculate variability?
Assess how much the peaks and troughs of the HR deviate from the baseline rate
How can variability be categorised?
Reassuring: 5-25bpm
Non reassuring: less than 5bpm between 30-50mins, more than 25bpm for 15-25 mins
Abnormal: less than 5bpm for more than 50mins, more than 25bpm for more than 25 mins, sinusoidal
What can cause reduced variability?
Fetal sleeping - should last no longer than 40mins (most common cause)
Fetal acidosis due to hypoxia - more likely if late decelerations also present
Fetal tachycardia
Drugs - opioids, benzodiazepines, methyldopa, magnesium sulphate
Prematurity - variability reduced afternoon earlier gestation
Congenital heart abnormalities
What are accelerations?
An abrupt increase in the baseline rate greater than 15bpm for greater than 15 seconds
Is the presence of accelerations reassuring?
Yes
Accelerations occurring alongside uterine contractions is a sign of a healthy fetus
The absence of accelerations with otherwise normal CTG is of uncertain significance
What are decelerations?
An abrupt decrease in baseline HR of greater than 15bpm for greater than 15 seconds
Why does the fetus reduce its HR in response to hypoxic stress?
To preserve myocardial oxygenation and perfusion
The reduction in HR to reduce myocardial demand is referred to as a deceleration- there are a number of different types
What are early decelerations?
They start when contraction begins and recover when uterine contractions stops
Caused by increased fetal intracranial pressure causing increased vagal tone, quickly resolves once contraction ends and pressure reduces
Considered physiological
What are variable decelerations?
Rapid fall in baseline HR with a variable recovery phase
They are variable in duration and may not relate to contractions
Most often seen in those with reduced amniotic fluid volume
What are variable decelerations usually caused by?
Umbilical cord compression
Umbilical vein compressed first, causing acceleration of fetal HR. Then umbilical artery occluded causing subsequent rapid deceleration. When pressure on cord reduced, another acceleration occurs and baseline returns
Accelerations before and after deceleration = shoulders of deceleration
- there presence indicates fetus not yet hypoxic and is adapting to reduced flow
Variable decelerations can sometimes be resolved if…
Mother changes position
The presence of persistent variable decelerations indicates a need for…
Close monitoring
Are variable decelerations without a shoulder more worrying?
Yes - suggests fetus becoming more hypoxic
What are late decelerations?
They begin at the peak of the uterine contraction and recover after the contraction ends
Indicates that there is insufficient blood flow to the uterus and placenta as a result blood flow to fetus significantly reduced causing fetal hypoxia and acidosis
Reduced uteroplacental blood flow can occur due to…
Maternal hypotension
Pre eclampsia
Uterine hyperstimulation
What is a prolonged deceleration?
Lasting more than 3 mins
If lasts between 2-3 mins = non reassuring
Longer than 3 mins immediately classed as abnormal
What is a sinusoidal pattern?
Rare, very concerning, high fetal morbidity and mortality Smooth wave like pattern Frequency: 2-5 cycles per minute Stable baseline around 120-160 No beat to beat variability
What does a sinusoidal pattern indicate?
Severe fetal hypoxia
Severe fetal anaemia
Fetal/maternal haemorrhage
How can the overall impression be classified?
Reassuring
Suspicious
Abnormal
