Fetal Monitoring

last authored: Oct 2011, David LaPierre
last reviewed:





Fetal monitoring is the assessment of various parameters of the fetus - normally the heart rate - to provide reassurance of well-being and identify potential causes for concern. Increased concern often prompts the health care team to make decisions regarding the speed and nature of delivery, such as through induction, augmentation, assisted delivery, or Caesarean section.


The fetal heart rate (FHR) increases and decreases largely due to autonomic signals from the brainstem, which also controls variability from beat to beat (Matsurra et al, 1996). A healthy fetus experiences transient and repetitive hypoxia, and a physiological drop in pH may also be seen. In fact, up to 80% of all labours result in abnormal or atypical FHR tracings at one time or another, without signifying life-treatening situations (Umstad, Permezel, and Pepperell, 1994). However, if a fetus is compromised for any reason, it's ability to withstand normal hypoxia is reduced. The goal of fetal monitoring is to identify evidence of fetal compromise during periods of hypoxia and to distinguish this from a normal fetal response.


An analogy to describe this is to consider an adult swimming across a pool while holding their breath (transient hypoxia). Normally this is not difficult. However, if the adult has just raced across a field and is out of breath (some compromise), he will have significant difficulty swimming under water across the pool.


Fetal oxygenation is affected by many factors:


  • respiratory disease
  • smoking
  • seizure
  • anemia
  • hypotension
  • regional anaesthesia
  • position
  • autoimmune conditions
  • heart disease


  • hyperstimulation (normal, prostaglandins, oxytocin)
  • abruption
  • chorioamnionitis
  • uterine rupture



  • oligohydramnios
  • cord compression or prolapse
  • intrauterine growth retardation


The fetus responds to hypoxia in a number of ways:

The goal of fetal monitoring is to identify evidence of worsening hypoxia and metabolic acidosis before organ damage occurs. This can include kidney failure, respiratory distress syndrome, necrotizing enterocolitis, liver damage, leukopenia, cardiomyopathy, and brain damage.




Descriptors of Fetal Heart Rate

The normal fetal heart rate is 110-160. Below this is bradycardia, and above this is tachycardia.



The baseline should be counted for at least 30 seconds, and preferably 60 seconds, between contractions. This provides a reference. The baseline should be reassessed between contractions throughout labour.



Variability describes fluctuation above or below the baseline. It depends on intact CNS and largely reflects vagal tone on the heart.

Decreased variability can be seen with:



A normal acceleration is defined as 15 bpm above baseline, lasting between 15-120 seconds in a fetus older than 32 weeks. For younger than 32 weeks, it is defined as 10 bpm above baseline for at least 10 seconds.



Decelerations are normally seen with fetal movement, and need not be worrisome. However, repetition of at least x declerations in 20 minutes does appear to carry increased risk. Decelerations lasting >1min are even more ominous.


Early decelerations are gradual decreases in heart rate, usually coinciding with the contraction. These are thought to be due to head compression and are almost always benign.


Late decelerations have their onset after the peak.

While false-positives are common, there are some rhythms that reliably signify fetal distress. A beat-to-beat variation in less than 5 bpm, absent accelerations, and late decelerations following uterine contractions is very worrying.


Variable decelerations have an abrupt onset, are a decrease of more than 15 bpm, and last for >15 sec. They can suggest cord compression. Complicated variable decelerations can be biphasic or prolonged.



Contractions: 5 or less in 10 min; fixed frequency and duration are rare.

duration <90 sec

configuration: regular, symmetrical

intensity: mild, moderate or strong (compare with the consistency of the nose, chin, forehead)

resting tone: soft, <15mmHg for >30 sec

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Intermittent Auscultation

FHR monitoring is done in over 80% of births in North America.

Intermittent auscultation (IA) does not measure baseline variability.


FHR should be evaluated:


Common patterns include:

Results need to be interpreted in the context of the total clinical picture.

A normal IA has a normal baseline and the presence of accelerations. The following are abnormal findings (Feinstein, Sprague, and Trepanier, 2000).


abnormal findings

potential causes and responses



monitor maternal vital signs and status

cord compression: reposition mother

fever: investigate and treat for infection

dehydration: provide fluids



monitor maternal vital signs and status

cord compression: reposition mother

cord prolapse: vaginal exam to investigate

hypovolemia: provide IV fluids



monitor maternal vital signs and status

reposition mother

evaluate for meconium

hypovolemia: provide IV fluids

consider maternal oxygen


If IA is abnormal, continued assessment is warranted. EFM (see below) should be considered. If abnormal results remain, consider delivery in an expedited fashion (ie Caesarean section).

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Electronic Fetal Monitoring (EFM)


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Nonstress Test

The nonstress test (NST) is an ultrasound assessment of fetal heart rate, measured through the mother's abdomen using a Doppler ultrasound. A tocometer is also used to measure uterine contractions.


The NST is the most widely-used test for fetal well-being. In many countries it is carried out routinely as term approaches. Testing was initially carried out one week apart, but this frequency has been increased in women who are postterm, carrying multiple fetuses, have diabetes or gestational hypertension, or have demonstrated fetal growth restriction. It is also indicated acutely if uteroplacental insufficiency or fetal distress is suspected.


A normal NST has at least two accelerations within 20 minutes. However, the test should proceed for at least 40 minutes before being labelled abnormal, in order to rule out sleep.






  • 110-160 bpm
  • 100-100 bpm
  • >160 bpm <30 min
  • rising baseline
  • <100 bpm
  • >160 bpm for >30 min
  • erratic baseline


  • 6-25 bpm
  • <5 for <40min
  • <5 bpm for 40-80 min


  • <5 for >80 min
  • >25 bpm for >10 min
  • sinusoidal


  • none
  • occasional variable for <30 sec
  • variable, 30-60 sec duration
  • variable, >60 sec
  • late decelerations

accelerations (term)

  • >2 of >15bpm, for 15 sec, in 20 min
  • <2 of >15 bpm, for 15 sec, in 40-80 min
  • <2 of >15 bpm, for 15 sec, in >80 min

accelerations (pre-term, <32 weeks)

  • >2 of >10bpm, for 10 sec, in 20 min
  • <2 of >10 bpm, for 10 sec, in 40-80 min

  • <2 of >10 bpm, for 10 sec, in >80 min



An abnormal (nonreactive) response is less than two accelerations over 20 minutes.

While normal NSTs are reassuring, 'insufficient acceleration' has a very high rate of false-negatives - up to 90%, by some studies (Devoe et al, 1986). However, it also warrants further testing via a biophysical profile, if available.

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Intrauterine Rescuscitation

If fetal monitoring of any type shows significant cause for concern, immediate action is required. Steps that should be taken include:

Monitor the mother's vitals, the fetal heart rate, and the fetal scalp pH or lactate if available. Once the infant is born, perform cord blood sampling (both arterial and venous) to assess fetal pH and well being during labour.

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Resources and References

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