Spectral analysis of fetal heart rate variability for fetal surveillance: review of the literature.

BACKGROUND Cardiotocography has a poor diagnostic value in detecting fetal acidosis. Spectral analysis of fetal heart rate variability can be used to monitor the fetal autonomic nervous system. OBJECTIVE To determine the value of spectral analysis for fetal surveillance. METHODS A systematic search was performed in the electronic databases CENTRAL (the Cochrane Library; 2007, Issue 3), PUBMED and EMBASE up to May 2007. Articles that described spectral analysis of human fetal heart rate variability and compared the energy in spectral bands with blood-gas values obtained by funipuncture or from the umbilical cord immediately postpartum were included. RESULTS Six studies met the inclusion criteria. The included studies were heterogeneous, various methods of spectral analysis and different frequency bands were used and the outcome measures varied. Five out of six studies showed a decrease in spectral energy in the low frequency (LF) band in case of fetal distress. An extremely low LF power had a sensitivity of 97.5% and a specificity of 86.1% to detect fetal distress. CONCLUSIONS Spectral analysis could be a promising method for fetal surveillance. Larger prospective studies are needed to determine the exact diagnostic value of spectral analysis. For further research, standardisation of spectral analysis is recommended. Studies should focus on real time monitoring.