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Sonicaid Team Operator’s Manual
73
Calculating peak-to-peak variation
The fetal heart rate record is analysed in one-minute intervals. Intervals containing a
deceleration or part of a deceleration are discarded, as are intervals with high signal
loss or artefact. For each remaining interval the maximum to minimum variation in
the fetal heart rate within that minute is calculated. The peak-to-peak variation is
defined as the maximum positive to maximum negative excursion from the fitted
baseline.
Fetal movements
Fetal movements recorded by the mother are counted and quantified per hour. This
number is given on the analysis report. In a normal trace, movements will be more
frequent during episodes of high variation than in episodes of low variation.
Fetal movements are recorded for twins’ traces, but not divided between twin 1 and
twin 2.
Contractions
The analysis defines a contraction as a rise in relative uterine pressure measurement
to greater than 16% from the baseline for 30 seconds or more. A count of contrac-
tions meeting this definition is made on the analysis report.
Signal loss
The system monitors the loss of fetal heart rate signal. Where there is a gap in the
trace due to signal loss, the analysis interpolates a straight line through the missing
section when fitting the baseline. When the analysis is running, the signal loss alarm
is fixed at 30%. The signal loss as a percentage of the whole record is given on the
analysis report. The analysis is not able to interpret the data if there is signal loss
> 80%.
If there is signal loss > 50% during either an acceleration or a deceleration of greater
than 20 lost beats, the acceleration or deceleration is not counted.
Errors
Signal artefacts are detected by the analysis, and counted as signal loss.