Electronic Fetal Monitoring definitions

Class,
            The previous post described the six components to interpretation of the fetal monitor tracing. This post contains the pattern definitions. We will be referring to the contents of these two posts as we explore fetal heart tracing interpretation and the significance of the various patterns to fetal well being.    

Pattern Definitions

Baseline • The mean FHR rounded to increments of 5 beats per minute during a 10-minute segment, excluding:

—Periodic or episodic changes

—Periods of marked FHR variability

—Segments of baseline that differ by more than 25 beats per minute

• The baseline must be for a minimum of 2 minutes in any 10-minute segment, or the baseline for that time period is indeterminate. In this case, one may refer to the prior 10-minute window for determination of baseline.

• Normal FHR baseline: 110–160 beats per minute

• Tachycardia: FHR baseline is greater than 160 beats per minute

• Bradycardia: FHR baseline is less than 110 beats per minute

Baseline variability • Fluctuations in the baseline FHR that are irregular in amplitude and frequency

• Variability is visually quantitated as the amplitude of peak-to-trough in beats per minute.

—Absent—amplitude range undetectable

—Minimal—amplitude range detectable but 5 beats per minute or fewer

—Moderate (normal)—amplitude range 6–25 beats per minute

—Marked—amplitude range greater than 25 beats per minute

Acceleration • A visually apparent abrupt increase (onset to peak in less than 30 seconds) in the FHR

• At 32 weeks of gestation and beyond, an acceleration has a peak of 15 beats per minute or more above baseline, with a duration of 15 seconds or more but less than 2 minutes from onset to return.

• Before 32 weeks of gestation, an acceleration has a peak of 10 beats per minute or more above baseline, with a duration of 10 seconds or more but less than 2 minutes from onset to return.

• Prolonged acceleration lasts 2 minutes or more but less than 10 minutes in duration.

• If an acceleration lasts 10 minutes or longer, it is a baseline change

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Early deceleration • Visually apparent usually symmetrical gradual decrease and return of the FHR associated with a uterine contraction

• A gradual FHR decrease is defined as from the onset to the FHR nadir of 30 seconds or more.

• The decrease in FHR is calculated from the onset to the nadir of the deceleration.

• The nadir of the deceleration occurs at the same time as the peak of the contraction.

• In most cases the onset, nadir, and recovery of the deceleration are coincident with the beginning, peak, and ending of the contraction, respectively.

Late deceleration • Visually apparent usually symmetrical gradual decrease and return of the FHR associated with a uterine contraction

• A gradual FHR decrease is defined as from the onset to the FHR nadir of 30 seconds or more.

• The decrease in FHR is calculated from the onset to the nadir of the deceleration.

• The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction.

• In most cases, the onset, nadir, and recovery of the deceleration occur after the beginning, peak, and ending of the contraction, respectively.

Variable deceleration • Visually apparent abrupt decrease in FHR

• An abrupt FHR decrease is defined as from the onset of the deceleration to the beginning of the FHR nadir of less than 30 seconds.

• The decrease in FHR is calculated from the onset to the nadir of the deceleration.

• The decrease in FHR is 15 beats per minute or greater, lasting 15 seconds or greater, and less than 2 minutes in duration.

• When variable decelerations are associated with uterine contractions, their onset, depth, and duration commonly vary with successive uterine contractions.

Prolonged deceleration • Visually apparent decrease in the FHR below the baseline

• Decrease in FHR from the baseline that is 15 beats per minute or more, lasting 2 minutes or more but less than 10 minutes in duration.

• If a deceleration lasts 10 minutes or longer, it is a baseline change.

Sinusoidal pattern • Visually apparent, smooth, sine wave-like undulating pattern in FHR baseline with a cycle frequency of 3–5 per minute which persists for 20 minutes or more.

Abbreviation: FHR, fetal heart rate.

Macones GA, Hankins GD, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring:

update on definitions, interpretation, and research guidelines. Obstet Gynecol 2008;112:661–6.