INTRAPARTUM FETAL MONITORING

FETAL HEART RATE

Cardiotocograph - CTG

 

The Abormal CTG

    

 

Fetal Bradycardia  

Moderate bradycardia: 100?109 bpm This range of baseline is not associated with hypoxia in the presence of accelerations, with normal baseline variability and no decelerations.

Abnormal bradycardia:  < 100 bpm

   

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    Fetal Tachycardia - (Variability is also reduced)

Moderate tachycardia:    161?180 bpm

This range of baseline is not associated with hypoxia in the presence of accelerations, with normal baseline variability and no decelerations.

Abnormal tachycardia:  > 180 bpm

     

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      Reduced Fetal Heart Rate Variability

Non-reassuring baseline: Less than 5 bpm for 40 minutes or more but less than 90 minutes variability.

Abnormal baseline: Less than 5 bpm for 90 minutes or more variability.

Physiological episodes of reduced heart rate variability of up to 30 minutes at 70 minute intervals can occur in the perinatal period in relation to quiet (non-REM) sleep.8401, 8601

There was a marked increase in the odds of cerebral palsy in the study by Nelson et al9601 seen in association with decreased baseline variability, although the limit for reduced baseline variability is not specified in the report. Samueloff et al9401 studied 2200 consecutive term singleton deliveriesfound that the majority of cases with adverse fetal outcome exhibited good FHR variability (mean, 80%). Low FHR variability was not common in newborns with adverse general outcome (mean, 11.5%). They concluded that FHR variability by itself cannot serve as the only indicator of fetal wellbeing. The presence of low variability should alert the physician; however, good FHR variability should not be interpreted as reassuring.  

Fetuses exhibiting low FHR variability commonly show lack of accelerations.8201

Absent and minimal baseline variability are associated with fetal asphyxia.9901    

   

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      Late Decelerations  

Decelerations: Transient episodes of slowing of FHR below the baseline level of more than 15 bpm and lasting 15 seconds or more

Late decelerations: Uniform, repetitive, periodic slowing of FHR with onset mid to end of the contraction and nadir more than 20 seconds after the peak of the contraction and ending after the contraction.12 In the presence of a non-accelerative trace with baseline variability less than 5 bpm, the definition would include decelerations less than 15 bpm.

There was a marked increase in the odds of cerebral palsy in association with multiple late decelerations (OR 3.9; 95% CI 1.7?9.3). This risk was further increased if both late decelerations and reduced baseline variability were present (OR 3.6;95% CI 1.9?6.7).9601

Late decelerations are significantly  associated with reduced Apgar scores.7501, 9101

Late decelerations had a high sensitivity for predicting subsequent abnormal neurological examinations, which were performed at 2, 4, 6, 9 and 12 months. Neurological sequelae seemed to be related to the duration of the abnormal fetal heart rate pattern.7501, 7801

Low et al, 9901concluded that there is a narrow 1-hour window of FHR patterns including minimal baseline variability and late or prolonged decelerations will predict fetal asphyxial exposure before decompensation and newborn morbidity.

   

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      Variable Decelerations

Variable decelerations: Variable, intermittent periodic slowing of FHR with rapid onset and recovery. Time relationships with contraction cycle are variable and they may occur in isolation. Sometimes they resemble other types of deceleration patterns in timing and shape.

Uncomplicated variable decelerations have not consistently been shown to be associated with poor neonatal outcome (reduced five-minute Apgar scores or metabolic acidosis).

Variable decelerations with the following additional features have been associated with poor adverse neonatal outcome in comparison with FHR traces with no decelerations or those with ?uncomplicated? variable decelerations:7802, 7901,8301, 9001, 9901

  • loss of acclerations
  • slow return to baseline FHR after the end of the contraction
  • prolonged increase of secondary rise in baseline rate
  • biphasic deceleration (variable followed by late component) - w-shaped deceleration
  • loss of variability during deceleration
  • bradycardia.

   

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    Prolonged Deceleration

Prolonged deceleration An abrupt decrease in FHR to levels below the baseline that lasts at least 60?90 seconds. These decelerations become pathological if they cross two contractions, i.e. greater than 3 minutes.

There is an association between prolonged bradycardia and acidosis.8402, 0201    

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     Sinusoidal Pattern

Sinusoidal pattern: a regular oscillation of the baseline long-term variability resembling a sine wave. This smooth, undulating pattern, lasting at least 10 minutes, has a relatively fixed period of 3?5 cycles per minute and an amplitude of 5?15 bpm above and below the baseline. Baseline variability is absent.

 

In uncompromised babies these patterns do not appear to be associated with poor outcome. However, in clinical practice, if this pattern appears in labour, clinically a feto-maternal haemorrhage must be excluded and, hence, these patterns must be viewed with suspicion.

Katz et al8302 concluded that patients with minor sinusoidal heart rate patterns may be managed expectantly, whereas on the rare occasion when a major sinusoidal pattern is seen expeditious delivery is justified.

 

Normal, Suspicious and Pathological Fetal Heart Traces

    

Normal A cardiotocograph where all four features fall into the reassuring category
Suspicious A cardiotocograph whose features fall into one of the non reassuring categories and the remainder of the features are reassuring
Pathological A cardiotocograph whose features fall into two or more non reassuring categories or one or more abnormal categories
   

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The aim of this web site is to provide a general guide and it is not intended as a substitute for a consultation with an appropriate specialist in respect of individual care and treatment.

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