[Spectral analysis of fetal heart rate variability]

To assess power spectral densities and power spectrum of FHR variability in two categories of fetal activity, quiescence and breathing movements, in pregnancies complicated by diabetes mellitus or intrauterine growth retardation.

The study group included 70 women, 35 in uncomplicated pregnancies and 35 with above-mentioned complications. The spectral analysis of FHR variability in fetal quiescence or breathing activity was performed. The power spectrum was analyzed at frequencies 0-1.0 Hz. Successively, the power spectral density was calculated. It has been presented the plots of spectral densities of beat-to-beat variabilities well during breathing episodes as "no breathing". Subsequently, the power spectra were calculated in both analyzed activities and groups.

The highest values of power spectral densities (0.118 +/- 0.025) at 0.6-0.8 Hz were found in uncomplicated pregnancies. In pregnancies complicated by diabetes mellitus (0.048 +/- 0.049) or IUGR (0.042 +/- 0.041) these values were statistically significantly. At 0.6 Hz and 0.8 Hz power spectra of FHR variability were lower in quiescence comparing to breathing activity, as well in uncomplicated as complicated pregnancies. At these frequencies power spectra during breathing movements were significantly lower in complicated pregnancies comparing to uncomplicated.

The results of this study confirm the usefulness of spectral analysis in the assessment of FHR variability. The observed disturbances may reflect an abnormal fetal reactivity. The evaluation of breathing and cardiovascular systems interaction allows to study indirectly the central nervous system that coordinates both activities.