What is Baseline Fetal Heart Rate (FHR)?

In this article, you will learn about baseline fetal heart rate including, fetal bradycardia and tachycardia.

Also, you’ll learn how to interpret fetal heart rate patterns and variabilities.

Related Article: Fetal Heart Rate Monitoring and VEAL CHOP MINE in Nursing

What is Baseline Fetal Heart Rate (FHR)?

The baseline fetal heart rate can be defined as the average heart rate of the fetus within 10 minutes.

The baseline rate should be within the normal range. That is 110–160 beats per minute.

The most common abnormalities in fetal heart rate are fetal bradycardia and fetal tachycardia.

Fetal Bradycardia

Fetal bradycardia is defined as a baseline fetal heart rate of less than 110 bpm and lasts longer than 10 minutes.

Causes of Fetal Bradycardia

  • Occiput posterior or transverse presentations
  • Prolonged cord compression
  • Cord prolapse
  • Anesthesia (epidural and spinal)
  • Maternal seizures
  • Rapid fetal descent
  • Fetal acidosis
  • Maternal hypotension
  • Prolonged maternal hypoglycemia
  • Fetal sepsis
  • Anomalies such as fetal heart conduction defect
  • Certain medications such as pethidine, antihypertensives (eg: methyldopa, propranolol), MgSO4

Fetal Tachycardia

Fetal tachycardia is defined as a baseline fetal heart rate of more than 160 bpm and lasts longer than 10 minutes.

Causes of Fetal Tachycardia

  • Drugs given to the mother such as (i) β-sympathomimetic agents used to inhibit preterm labor (isoxsuprine, ritodrine); (ii) Vagolytic: atropine
  • Fetal and/or maternal anemia
  • Fetal and/or maternal infection
  • Maternal dehydration
  • Maternal anxiety
  • Maternal hyperthyroidism
  • Fetal hypoxia
  • Fetal tachyarrhythmia
  • Chorioamnionitis

How to interpret baseline fetal heart rate patterns?

Baseline fetal heart rate can be interpreted as reassuring, non-reassuring, or ominous signs.

Reassuring SignsNon-reassuring SignsOminous Signs
a. Normal baseline (110–160 bpm)a. Fetal tachycardia (>160 bpm)a. Fetal tachycardia with loss of variability
b. Moderate bradycardia (100–120 bpm); good variabilityb. Moderate bradycardia (100–110 bpm); lost variabilityb. Prolonged marked bradycardia (<90 bpm)
c. Good beat-to-beat variability and fetal accelerationsc. Absent beat-to-beat variabilityc. Severe variable decelerations (<70 bpm)
d. Marked bradycardia (90–100 bpm)d. Persistent late decelerations

e. Moderate variable decelerations
Interpretation of FHR patterns


What is baseline fetal heart rate (FHR) variability? 

Baseline fetal heart rate variability refers to the fluctuation between fetal heartbeats. It doesn’t include accelerations and decelerations.

FHR Variability is a normal reflex that occurs as a result of the interaction between the parasympathetic and sympathetic nervous systems. It is an important clinical indicator that is predictive of fetal acid-base balance and cerebral tissue perfusion.

Baseline FHR variability can be short-term or long-term.

The presence of short-term variability is classified either as “present” or “absent”. And typically, it is an indication of a well-oxygenated and non-acidemic fetus.

Visually you can see the presence or absence of short-term variability.

To do that, evaluate the roughness or smoothness of the fetal heart tracing line. If roughness is present in the baseline, short-term variability is present. And it is absent if it is smooth.

Long-term variability is the waviness or rhythmic fluctuations. Its described as cycles per minute and the frequency of cycles is 3 to 6 per minute.

Long-term variability is categorized as:

  • Absent – amplitude undetectable
  • Mini­mal – amplitude is between 0 to 5 bpm
  • Moderate – amplitude is between 6 to25 bpm
  • Marked or salutatory – amplitude is above 25 bpm

Causes of decreased FHR variability

Causes of decreased FHR variability include:

  • Fetal hypoxia
  • Fetal acidosis
  • Drugs such as opiates, benzodiazepines, methyldopa, and magnesium sulfate.
  • Congenital abnormalities
  • Fetal sleep: this is the most common cause and it should not last longer than 40 minutes.
  • Prematurity: variability is reduced at earlier gestation (<28 weeks)
  • Fetal tachycardia

How to interpret fetal heart variability?

Variability can be interpreted as reassuring, non-reassuring, or abnormal. 

The variability is Reassuring, if it is between 5 – 25 bpm.

It is non-reassuring if:

  • variability is less than 5 bpm for between 30-50 minutes, or
  • more than 25 bpm for 15-25 minutes,

It is abnormal if:

  • variability less than 5 bpm for more than 50 minutes
  • more than 25 bpm for more than 25 minutes, or
  • sinusoidal

Periodic Baseline Changes

Periodic baseline changes are temporary, recurrent changes made in response to a stimulus such as a contraction. The FHR shows a pattern of acceleration or deceleration in response to most stimuli.


Acceleration is defined as a momentary increase in fetal heart rate above the baseline.

Characteristics of Acceleration

  • visually apparent with elevations of FHR of at least 15 bpm above the baseline
  • usually, last longer than 15 seconds but not for longer than 2 minutes
  • prolonged acceleration is when it lasts longer than 2 minutes but less than 10 minutes
  • if acceleration lasts more than 10 minutes, it is considered a change in baseline

Nursing Intervention for Acceleration

Acceleration is typically a sign of reassuring fetal status and no special nursing interventions are needed.

Early Decelerations

Early deceleration is characterized by a gradual decrease and return to the baseline of the FHR associated with a uterine contraction. 

The onset of early deceleration to nadir (lowest point) is usually more than or equal to 30 seconds. The nadir occurs at the same time as the peak of the contraction.

Causes of Early Deceleration

Causes for early deceleration is fetal head compression.

Nursing Intervention for Early Deceleration

Early decelerations are not indicative of fetal distress. Therefore, special nursing intervention is not required.

Late Decelerations

Late decelerations can be defined as temporary decreases in FHR that occur after a contraction begins.

The FHR returns to normal only after the contraction has ended completely. Delayed timing of the deceleration occurs with the nadir of the uterine contraction.

The late deceleration is a sign of uteroplacental insufficiency and poor perfusion.

Causes for Late Deceleration

Causes for late deceleration include:

  • maternal hypotension
  • gestational hypertension
  • placental aging secondary to diabetes
  • post-maturity
  • hyperstimulation via oxytocin infusion
  • maternal smoking
  • anemia
  • cardiac disease

Nursing Interventions for Late Deceleration

Nursing InterventionRationale
Turning the mother on her left sideIncreases placental perfusion
Administer oxygen by maskIncreases fetal oxygenation
Increasing the IV fluid rateImproves intravascular volume
Assessing mother for any underlying contributing causesTo identify and address underlying causes
Provide reassurance that interventions are to effect pattern changeHelps to reduce mental stress and anxiety
Nursing intervention for late deceleration

Additional nursing interventions include:

  • informing the primary healthcare provider about pattern change
  • reducing or stopping the Oxytocin drip
  • accurate documentation

Variable Decelerations

Variable deceleration is defined as an abrupt decrease of FHR from the onset of the deceleration to the beginning of the FHR nadir of <30 seconds.

The decrease in FHR is 15bpm or more. And lasts ≥ 15 seconds and less than 2 minutes.

The shape of variable decelerations maybe U, V, or W, or they may not resemble other patterns.

It becomes a non-reassuring sign if:

  • FHR decreases to less than 60 bpm
  • persists at that level for at least 60 seconds
  • repetitive decrease of FHR

Cause for Variable Deceleration

Cord compression

Nursing Interventions for Variable Deceleration

Nursing InterventionRationale
Reposition the motherTo relieve compression on the cord
Administer oxygen by maskIncreases fetal oxygenation
Increasing the IV fluid rateImproves intravascular volume
Assessing mother for any underlying contributing causesTo identify and address underlying causes
Provide reassurance that interventions are to effect pattern changeHelps to reduce mental stress and anxiety
Nursing intervention for variable deceleration

Additional nursing interventions same as the late deceleration interventions.

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