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 Signs | Non-reassuring Signs | Ominous 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 variability | b. Moderate bradycardia (100–110 bpm); lost variability | b. Prolonged marked bradycardia (<90 bpm) |
| c. Good beat-to-beat variability and fetal accelerations | c. Absent beat-to-beat variability | c. Severe variable decelerations (<70 bpm) |
| d. Marked bradycardia (90–100 bpm) | d. Persistent late decelerations | |
| e. Moderate variable decelerations |
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
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 Intervention | Rationale |
|---|---|
| Turning the mother on her left side | Increases placental perfusion |
| Administer oxygen by mask | Increases fetal oxygenation |
| Increasing the IV fluid rate | Improves intravascular volume |
| Assessing mother for any underlying contributing causes | To identify and address underlying causes |
| Provide reassurance that interventions are to effect pattern change | Helps to reduce mental stress and anxiety |
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 Intervention | Rationale |
|---|---|
| Reposition the mother | To relieve compression on the cord |
| Administer oxygen by mask | Increases fetal oxygenation |
| Increasing the IV fluid rate | Improves intravascular volume |
| Assessing mother for any underlying contributing causes | To identify and address underlying causes |
| Provide reassurance that interventions are to effect pattern change | Helps to reduce mental stress and anxiety |
Additional nursing interventions same as the late deceleration interventions.
