Baseline heart rate is the mean fetal heart rate during the 10 minute segment of time, excluding periodic changes. Changes in FHR and normal periodic changes of FHR are related to the following:
Uterus hyperstimulation (commonly caused by medications)
Fetus head compression
Umbilical cord and compression
Placental insufficiency
Normal baseline FHR = 110 - 160 beats/minute.
Tachycardia > 160 beats per minute is most commonly related to medications (B agonist: (terbutaline, ritodrine).
Bradycardia <110 beats per minute is most commonly related to medication (BB or local anesthetics).
Periodic changes in heart rate include the following:
Accelerations: Abrupt increases in fetal heart rate lasting less than 2 minutes that are unrelated to contractions. They always occur in response to fetal movements and are always reassuring.
Early decelerations: Gradual decreases in fetal heart rate beginning and ending simultaneously with contractions. There occur in response to fetal head compression.
Variable decelerations: Abrupt decreases in the fetal heart rate that are unrelated to contractions. These are related to umbilical cord compression. Severe variables are non-reassuring and indicate fetal acidosis.
Late deceleration: Gradual decreases in fetal heart rate and delayed in relation to contractions. These are related to utero-placental insufficiency. All late decelerations are non-reassuring and indicate fetal acidosis.
Reassuring fatal heart rate tracing:
Baseline fetal heart rate: 110 to 160 beats per minute
Accelerations are present
Decelerations are absent
Beat to beat variability present
Non-reassuring fetal heart rate tracing:
Baseline fetal heart rate shows tachycardia or bradycardia
No accelerations
Variable or late deceleration are present.
Beat to beat variability is absent.
Variability: Beat-to-beat fetal heart rate normally has variability. Normal variability is 6-25 bpm. Absence of variability is a nonreassuring pattern.
Stepwise approach to nonreassuring fetal tracings:
Examine the electronic fetal monitoring strip (EFM): Look for nonreassuring pattern.
Identify nonhypoxic causes that can explain the abnormal findings. Most common are medications, particularly beta-agonists or beta blockers.
Begin intrauterine resuscitation as follows:
Discontinue medications (e.g., oxytocin)
Give IVF, NS boluses
Provide high flow oxygen
Change patient’s position to left lateral recumbent.
Vaginal exam to rule out prolapsed cord
Perform scalp stimulation to observe for accelerations (reassuring)
Prepare for delivery if EFM tracing dozen or normalize