Share This Link

A baseline fetal heart rate range of 80–100 bpm is considered fetal bradycardia. Fetal bradycardia is defined as a baseline FHR persistently below 110 bpm for 10 minutes or longer and can indicate significant fetal distress, such as severe hypoxia, congenital heart block, or profound maternal hypotension, necessitating urgent evaluation and intervention.

A baseline fetal heart rate range of 100–120 bpm, while closer to normal, still falls within the definition of fetal bradycardia if sustained for 10 minutes or more. Although less severe than rates below 100 bpm, it warrants careful assessment to rule out underlying causes of fetal compromise, as it deviates from the established normal range.

A baseline fetal heart rate range of 160–180 bpm is indicative of fetal tachycardia, which is defined as a baseline FHR persistently above 160 bpm for 10 minutes or longer. Fetal tachycardia can be a sign of various issues including maternal fever, maternal dehydration, chorioamnionitis, fetal hypoxia, or maternal use of certain medications, and requires clinical investigation.

Normal fetal well-being is typically indicated by the presence of moderate variability, which is an amplitude range of 6-25 bpm. Absent variability, conversely, deviates significantly from this normal pattern and is a sign of potential fetal distress, not well-being.

Fetal movement often elicits accelerations in the fetal heart rate, which are transient increases in FHR above the baseline. While fetal movement can influence FHR, it is associated with normal variability or accelerations, not absent variability. Absent variability indicates a lack of autonomic nervous system response, which would contradict the presence of normal fetal movement.

Uterine contractions themselves are associated with changes in FHR patterns, such as early, late, or variable decelerations, depending on the physiological response. However, uterine contractions directly cause changes in the FHR pattern (periodic changes), and do not inherently cause or explain absent variability in the baseline FHR. Absent variability reflects an underlying state independent of the immediate mechanical effects of a contraction.

Early decelerations are typically associated with fetal head compression during uterine contractions. They are characterized by a gradual decrease in FHR that mirrors the contraction, with the nadir of the deceleration coinciding with the peak of the contraction. This is generally considered a benign finding due to vagal stimulation and does not indicate uteroplacental insufficiency.

Variable decelerations are characterized by an abrupt, often irregular, decrease in FHR of varying shape, duration, and magnitude. These are most commonly caused by umbilical cord compression, which leads to a transient decrease in umbilical blood flow. While they can be concerning if severe or prolonged, their primary etiology is mechanical compression of the cord, not uteroplacental insufficiency.

A prolonged deceleration is a marked decrease in FHR of at least 15 bpm below the baseline, lasting for 2 minutes or more but less than 10 minutes. These decelerations can be caused by a variety of acute events that severely compromise fetal oxygenation, such as sustained umbilical cord compression, maternal hypotension, uterine tachysystole, or placental abruption. While uteroplacental insufficiency can contribute to a compromised fetus being less resilient to such events, it is not the primary or sole cause typically associated with the pattern of a prolonged deceleration itself.