Definition of Late Decelerations
Late decelerations look similar to early decelerations in shape and uniformity, but the timing is completely different. A late deceleration is defined as a visually apparent, usually symmetrical gradual decrease and return to the baseline fetal heart rate associated with uterine contractions (NICHD, 2008). The onset, nadir, and recovery of the deceleration follow the beginning, peak, and end of the contraction, sometimes by as much as 30 seconds. Late decelerations are a response to inadequate oxygen exchange in the intervillous space (uteroplacental insufficiency).