An acceleration > 2 minutes but less than 10 minutes in duration is called a prolonged acceleration. An acceleration lasting > 10 minutes is a baseline change. Accelerations may be further categorized as episodic or periodic. Episodic accelerations occur independent of uterine contractions. Periodic accelerations are associated with uterine contractions. Accelerations may be present or absent in an otherwise normal category I fetal heart rate tracing..
The presence of either spontaneous or stimulated FHR accelerations reliably predicts the absence of fetal metabolic acidemia at the time they are observed provided the heart rate being recorded is truly the fetus and not the mother [1,6]. Periodic accelerations caused by partial umbilical cord compression are not as reassuring as episodic accelerations since continued cord compression may cause progression to a category II or category III tracing . A rise in the fetal heart rate provoked by fetal scalp stimulation during a prolonged deceleration is of uncertain significance since the rise in heart rate is not by definition an acceleration.
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