A New Computerized Analysis to Precisely Evaluate Heart Rate Variability During the Nonstress Test

ABSTRACT

The study was conducted to assess whether the power spectrum analysis of fetal heart rate (FHR) data obtained with a cardiotocograph provides more than visual judgment of nonstress test (NST) tracing to predict fetal well-being. A total of 71 FHR data were obtained from 44 healthy pregnant women with normally grown fetuses and 11 pregnant women with pregnancy-induced hypertension. Power spectrum analysis was performed for the 8192 points of the instantaneous heart rates derived from these FHR data. Abnormal perinatal outcome was defined when at least one of the followings were present at birth: Cesarean delivery for nonreassuring FHR pattern and umbilical artery cord PH ≤ 7.15, delivery at ≤ 32 weeks for fetal compromise, neonatal seizures within the first 72 hours of life, respiratory distress at 36 weeks or more, 5-minute Apgar score < 7 and stillbirth. The total power of the 8192 points without considering gestational weeks was 256.3 ± 65.6 normalized units (NU) ˙ Hz in the fetuses with good outcomes (n = 47), while that of the abnormal fetuses (n = 8) was 148.5 ± 54.6 NU ˙ Hz. There is a significant difference between the two values (p < 0.00001). When the abnormal value of the total power of the 8192 points was defined as < 200 NU ˙ Hz, the sensitivity on the prediction of fetal outcome using this method was 81.8%, significantly higher than that of the nonstress test tracing (p < 0.05). The power spectrum analysis of the large amount of FHR data obtained with a cardiotocograph permits a better assessment of the fetal well-being and may be suitable for the screening test because of no additional manpower to the current NST.

KEYWORDS

Spectrum analysis - fetal well-being - nonstress test

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