Periodic spectral components of fetal heart rate variability reflect the changes in cord arterial base deficit values: a preliminary report.

Fetal distress changes the function of the autonomic nervous system. These changes are reflected in the fetal heart rate and can be quantified with power spectrum analysis of heart rate variability. The purpose of this study was to find out whether spectral components of fetal heart rate variability (FHRV) during labor are associated with fetal cord arterial base deficit values at birth. The association between FHRV and umbilical cord arterial base deficit was studied in 14 singleton fetuses with normal pregnancy at 35-40 weeks of gestation. Fetal ECG was recorded by scalp-electrode using a STAN Fetal ECG monitor (Cinventa Ab, Mölndal, Sweden). FHRV was quantified by computing Fast-Fourier-transformed heart rate (HR) spectra at three frequency bands: low-frequency (LF) 0.03-0.07 Hz, mid-frequency (MF) 0.07-0.13 Hz and high-frequency (HF) 0.13-1.0 Hz. We found that total FHRV and MF FHRV were lower in fetuses with cord arterial base deficit 8 to 12 mmol/L in comparison to the fetuses with normal cord arterial base deficit value (P=0.02 and P=0.01, respectively). A linear correlation was found between the spectral densities and the cord arterial base deficit values (r=0.4 and r=0.6, respectively). We conclude that the results suggest changes in the autonomic nervous cardiac control in fetuses with cord arterial base deficit between 8 to 12 mmol/L. The clinical applicability of our observations on FHRV in predicting fetal distress remains to be further studied.