This tracing contains multiple decelerations. Decelerations are characterized by a decrease from baseline of at least 15 beats per minute (BPM), lasting at least 15 s and no longer than 2 min. A deceleration is considered prolonged when it lasts beyond 2 min. Specifically, the tracing above depicts variable decelerations. Variable decelerations have inconsistent shape and timing in relationship to uterine contractions. Variable decelerations are caused by cord compression.

By contrast early decelerations occur in sync with contractions such that the nadir of the deceleration occurs at the peak of the contraction. Early decelerations relate to fetal head compression during contraction. Late decelerations are also closely associated with contractions with the decrease in heart rate beginning immediately after the peak of the contraction, mirroring the contraction in shape. Late decelerations represent uteroplacental insufficiency and may be due to hypotension or other factors [1].

Fetal heart rate is a surrogate measurement for fetal oxygenation and acid/base status. Anytime there is a deceleration, there is presumed to be a decrease in delivery of oxygen to the fetus. This may be mild and of little concern, as in the case of early decelerations, or clinically significant as in the case of late, variable, or prolonged decelerations. With repeated decelerations, hypoxia may lead to acidosis, which could eventually lead to neurologic injury. In particular injury may occur when umbilical artery pH decreases below 7.0 or there is a base deficit of greater than 12 [2].

There is no evidence in the literature to support older terms for describing decelerations, such as the presence of “shoulders,” variable with late component, or shape of the deceleration. Similarly it is a distraction to categorize the deceleration pattern by severity.

The absence of variability is a marker for acidemia. Moderate variability or the presence of accelerations is a very sensitive measure for a normal acid/base status. This strip still has the presence of moderate variability, defined by changes in the baseline heart rate that are nonuniform, which essentially rules out metabolic acidosis.