FHR decelerations or bradycardia episodes come in three types. Early decelerations are normal and common. These decelerations are called early because they occur early during a uterine contraction . The FHR rarely goes below 100 beats per minute. The cause of these decelerations is head compression during uterine contractions.
Late decelerations cause more concern.
They are called late because they first appear at or after the peak of the uterine contraction. The FHR improves only after the contraction has stopped. These FHR decelerations may be mild or severe based on how low the FHR goes and how long it takes for the FHR to recover. It is thought to be caused by reduced blood flow to the uterus and placenta during a contraction. Variable decelerations are a common type of FHR deceleration in labor and are caused by umbilical cord compression.