Fetal Heart Rate Monitoring

Accelerations
The FHR increases more than 15 BPM for more than 15 seconds. Accelerations usually appear as smooth patterns on electronic fetal monitoring and are a good indication of fetal well-being. Accelerations may be triggered in the normal mature fetus by fetal body motion, sounds, stimulation of the fetal scalp, and other stimuli.

Early decelerations
Early decelerations are normal and common. The deceleration pattern matches the contraction with the most deceleration occurring at the peak of the contraction. The FHR rarely goes below 100 beats per minute. The cause of these decelerations is head compression during uterine contractions.

Late decelerations
Decrease in FHR from the baseline rate with a lag time of greater than 20 seconds from the peak of the contraction to the nadir of FHR deceleration.They first appear at or after the peak of the uterine contraction. The FHR improves only after the contraction has stopped. These 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. Late deceleration is associated with uteroplacental insufficiency and is a consequence of hypoxia and metabolic abnormalities. Late deceleration is the most ominous fetal heart rate pattern.

Variable deceleration
Variable decelerations are a common type of FHR deceleration in labor and are caused by umbilical cord compression. Up to 80% of fetuses will have variable decelerations during labor. The significance of the these decelerations depends on how low the heart rate drops and how long the episode lasts. Variable decelerations are caused by umbilical cord compression and are classified as severe if they last more than 60 seconds or lead to a FHR of less than 90 BPM.