Analysis of fetal heart rate variability obtained by magnetocardiography

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

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.

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).

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.