Late Decelerations (labor and delivery) A “deceleration” describes a decrease in the heart rate of the fetus from its baseline heartrate. “Late decelerations” are described as a transient decrease in the fetal heart rate occurring at or after the peak of a uterine contraction. Late decelerations may represent some degree of utero-placental insufficiency. All blood flow in and out of the intravillious space stops briefly during a contraction.