Causes of fetal tachycardia
Fetal hypoxia
Chorioamnionitis
Hyperthyroidism
Fetal or maternal anaemia
Fetal tachyarrhythmia
causes of fetal bradycardia (100 to 120)
- Postdate gestation
- Occiput posterior or transverse presentations
causes of sever bradycardia less than 80
- Prolonged cord compression
- Cord prolapse
- Epidural and spinal anaesthesia
- Maternal seizures
- Rapid fetal descent
classifications of variability
reassuring (5 to 25 bpm)
non reassuring (less than 5 bpm between 30 and 50 minutes or more than 25bpm for 15 to 25 minutes)
abnormal (less than 5bpm for more than 50 minutes or more than 25bpm for more than 25 minutes or sinusoidal curve)
causes of decreased variability
- 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
what is an acceleration
Accelerations are an abrupt increase in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.
the presence of accelerating 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.
what are decelerations
Decelerations are an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.
what are early decelerations
Early decelerations start when the uterine contraction begins and recover when uterine contraction stops.
what are variable decelerations
Variable decelerations are observed as a rapid fall in baseline fetal heart rate with a variable recovery phase.
what are late decelerations
Late decelerations begin at the peak of the uterine contraction and recover after the contraction en
what is classified as a prolonged deceleration
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.
summary on sinusoidal pattern on CTG
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
What are the charecteritics of a sinusoidal pattern
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
what is a reassuring CTG
Baseline heart rate
110 to 160 bpm
Baseline variability
5 to 25 bpm
Decelerations
None or early
Variable decelerations with no concerning characteristics for less than 90 minute
what is a non reassuring CTG
Baseline heart rate
Either of the below would be classed as non-reassuring:
- 100 to 109 bpm
- 161 to 180 bpm
Baseline variability
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
Decelerations
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.
Causes of a fetal bradycardia
What is a abnormal CTG
Baseline heart rate
Either of the below would be classed as abnormal:
Below 100 bpm
Above 180 bpm
Baseline variability
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
Sinusoidal
Decelerations
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
what are the causes of early decelerations
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
what is the cause of a variable deceleration
Variable decelerations are usually caused by umbilical cord compression. The mechanism is as follows:
- The umbilical vein is often occluded first causing an acceleration of the fetal heart rate in response.
- Then the umbilical artery is occluded causing a subsequent rapid deceleration.
- When pressure on the cord is reduced another acceleration occurs and then the baseline rate returns
what are the causes of late decelerations
- Maternal hypotension
- Pre-eclampsia
- Uterine hyperstimulation
what does a sinusoidal curve indicate
- Severe fetal hypoxia
- Severe fetal anaemia
- Fetal/maternal haemorrhage
