“Variability” in fetal heart rate (FHR) refers to the beat-to-beat changes in heart rate that occur naturally and are considered a marker of fetal well-being. Although a fetus’s heart rate usually stays within a range of 110 to 160 beats per minute (bpm) it typically doesn’t stay at the same rate all the time. Variability is usually seen as periodic acceleration and deceleration of the heart rate and can be measured by looking at the change in FHR over time.
Acceleration is defined as an abrupt increase in fetal heart rate of at least 15 bpm above the baseline for at least 15 seconds. Deceleration is defined as a decrease in fetal heart rate of at least 15 bpm below the baseline for at least 15 seconds. Baseline FHR is the fetal heart rate when it is not undergoing an acceleration or deceleration.
Variability is thought to be a good indicator of fetal well-being because it shows that the fetus is responding to its environment and is able to change its heart rate in response to stimuli. A lack of variability on the other hand may be a sign of distress and can be an indicator of poor fetal health.
There are different types of variability that can be seen on an FHR tracing including sinusoidal periodic and random variability. Sinusoidal variability is a smooth repetitive wave-like pattern that is thought to be caused by respiratory movements of the fetus. Periodic variability is also a wave-like pattern but it is not as regular as sinusoidal variability and is usually caused by changes in blood flow due to uterine contractions. Random variability is irregular and unpredictable and is thought to be caused by different factors including fetal movements changes in maternal blood pressure and changes in the level of carbon dioxide in the maternal blood.
Variability is usually assessed by looking at a strip of paper or electronic fetal monitoring tracing that shows the FHR over time. The tracing is divided into 10-second intervals and the variability is reported as the number of beats per minute (bpm) that the FHR changes by over the course of those 10 seconds. A high degree of variability is usually defined as a change of at least 5 bpm.
Variability is usually considered to be a good thing as it shows that the fetus is reacting to its environment. However there are some situations where a high degree of variability can be a cause for concern. For example if the variability is accompanied by late decelerations (a decrease in fetal heart rate that occurs after a contraction) it may be a sign of uteroplacental insufficiency which is a condition in which the placenta is not able to adequately provide oxygen and nutrients to the fetus.
If you are pregnant and have any concerns about your FHR tracing be sure to discuss them with your healthcare provider.
What is variability in fetal heart rate?
Variability in fetal heart rate is the beat-to-beat changes in the heart rate.
What is the normal range for variability in fetal heart rate?
The normal range for variability in fetal heart rate is 5-25%.
Why is variability in fetal heart rate important?
Variability in fetal heart rate is a good indicator of fetal well-being.
How is variability in fetal heart rate measured?
Variability in fetal heart rate is measured by Accelerometry.
What are the causes of low variability in fetal heart rate?
Low variability in fetal heart rate can be caused by maternal factors such as dehydration hypoxia and maternal smoking.
It can also be caused by fetal factors such as growth restriction anemia and fetal hypoxia.
What are the consequences of low variability in fetal heart rate?
Low variability in fetal heart rate is associated with an increased risk of neonatal morbidity and mortality.
What are the causes of high variability in fetal heart rate?
High variability in fetal heart rate can be caused by maternal factors such as caffeine consumption and maternal obesity.
It can also be caused by fetal factors such as fetal tachycardia and fetal head compression.
What are the consequences of high variability in fetal heart rate?
High variability in fetal heart rate is associated with an increased risk of neonatal morbidity and mortality.
What is the relationship between variability in fetal heart rate and neonatal acidosis?
Low variability in fetal heart rate is a risk factor for neonatal acidosis.
What is the relationship between variability in fetal heart rate and fetal distress?
Low variability in fetal heart rate is a risk factor for fetal distress.
What is the relationship between variability in fetal heart rate and meconium aspiration syndrome?
Low variability in fetal heart rate is a risk factor for meconium aspiration syndrome.
What is the relationship between variability in fetal heart rate and birth asphyxia?
Low variability in fetal heart rate is a risk factor for birth asphyxia.
What is the relationship between variability in fetal heart rate and Cesarean delivery?
Low variability in fetal heart rate is a risk factor for Cesarean delivery.
What is the relationship between variability in fetal heart rate and stillbirth?
Low variability in fetal heart rate is a risk factor for stillbirth.
What is the relationship between variability in fetal heart rate and neonatal intensive care unit admission?
Low variability in fetal heart rate is a risk factor for neonatal intensive care unit admission.
