••• Chapter 4^ Antepartum Management and Fetal Surveillance^47
❍ What is the largest increased risk associated with continuous electronic FHR monitoring?
Increased cesarean section rate.
FETAL HEART RATE PATTERNS AND DEFINITIONS
❍ What is the baseline FHR?
The mean FHR rounded to increments of 5 bpm during a 10-minute window. There must be at least 2 minutes
of identifiable baseline segments. Normal baseline ranges from 110 to 160 bmp. Bradycardia when baseline is
<110 bpm and tachycardia when baseline is >160 bpm.
❍ What is variability?
Fluctuations in the baseline FHR that are irregular in amplitude and frequency. Quantified as the amplitude from
peak to trough.
❍ What are the different degrees of variability?
- Absent: Amplitude range undetectable.
- Minimal: Amplitude range 1 to 5 bpm.
- Moderate: Amplitude range 6 to 25 bpm.
- Marked: Amplitude range >25 bpm.
❍ What is an acceleration?
Visually apparent abrupt increase in FHR. Onset of acceleration to peak >30 seconds. A prolonged acceleration
is ≥2 minutes but <10 minutes long.
❍ What is a deceleration? And how are they classified?
Visually apparent decrease in FHR. Decelerations are classified into early, variable, late, and prolonged
decelerations.
❍ What is an early deceleration?
Visually apparent, symmetrical, gradual decrease and return of FHR baseline associated with a uterine contraction.
Cause: Fetal head compression
Characteristics:
- Onset to nadir ≥30 seconds.
- Nadir of deceleration occurs at the same time as the peak of the contractions.
❍ What is a variable deceleration?
Visually apparent abrupt decrease in FHR. Cause: Umbilical cord compression
Characteristic:
- Onset to nadir <30 seconds.
- Decrease in FHR is ≥15 bpm, lasting >15 seconds and >2 minutes in duration.