Baseline • Fluctuations in the baseline FHR that are irregular in amplitude and frequency variability • Variability is visually quantified as the amplitude of peak-to-trough in beats per minute -Absent: amplitude range undetectable -Minimal: amplitude range detectable but 5 beats per minutes 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 bpm or more above baseline, with a duration of 15 sec or more but less than 2 minutes from onset to return
Before 32 weeks, an acceleration has a peak of 10 bpm or more above baseline, with a duration of 10 seconds or more but less than 2 minutes from onset to return
If an acceleration lasts 10 minutes or longer, it is a baseline change
Early deceleration • Visually apparent usually symmetrical gradual decrease and return of the FHR associated with a
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
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 deceleration • 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 contraction, their onset, depth, and duration commonly vary with successive uterine contractions
Prolonged • Visually apparent decrease in the FHR below the baseline deceleration • Decrease in FHR from the baseline that is 15 per minute or more, and less than 2 minutes in duration • If a deceleration last 10 minutes or longer, it is a baseline change
Sinusoidal pattern • Visually apparent, smooth, sine wave-line undulating pattern in FHR baseline with a cycle frequency of 3-5 per minute which persists for 20 dinutes or more
FHR = fetal heart rate. Data from Macones, 2008.
FIGURE 24-6 Schematic representation of short-term beat-tobeat variability measured by a fetal scalp electrode. t time interval between successive fetal R waves. (Adapted with permission from Klavan M, Laver AT, Boscola MA: Clinical concepts of fetal heart rate monitoring. Waltham, Hewlett-Packard, 1977.)
FIGURE 24-5 Fetal bradycardia measured with a scalp electrode (upper paneD in a pregnancy complicated by placental abruption and subsequent fetal death. Concurrent uterine contractions are shown in the lower panel.
rising blood lactate level and severe metabolic acidemia, induces a prolonged fall in heart rate (hakor, 2009).