Analysis of fetal heart rate variability obtained by magnetocardiography.

Objective: To obtain fetal magnetocardiogram (fMCG) recordings in preterm fetuses in both shielded and unshielded clinical settings.

Methods: Seventeen fMCG recordings were obtained from 6 low-risk fetuses of 26-35 weeks' postmenstrual age. The superconducting quantum interference device biomagnetometer was positioned over the gravid abdomen, and the signals, associated with the bioelectrical activity of the fetal heart, were digitized at a sampling rate of 1 kHz. The fMCG signal was recorded for 5 minutes along with the reference maternal electrocardiogram in both the shielded and unshielded environment. A nonsyntactic QRS detection algorithm based on Pan-Tompkins scheme was employed for extracting fetal RR time series.

Results: The growth rate of 1.97 decibels (dB) exhibited by the low-frequency (LF) band is almost 2 1/2 times that of the high-frequency (HF) band. HF/LF power ratio was calculated to have a negative growth rate of -0.17 dB/wk (P = .004). Total power increased at approximately 1.35 dB/wk (P = .031).

Conclusions: Consistent with the literature, the total power, or the variance, as well as the LF and HF powers independently, indicates an increasing trend with increasing postmenstrual age.