Fetal heart rate monitoring by magnetocardiograms.

The magnetic field produced by the fetal heart magnetocardiogram (FMCG) was measured by a single channel SQUID biogradiometer in an unshielded environment. FMCG amplitude ranged from 1 to 4 pT. Instantaneous fetal heart rate and averaged FMCG waveforms were computed. Spectral analysis was used to quantify fetal heart rate variability, and revealed peaks from 0.5 to 1.0 Hz, consistent with respiratory sinus arrhythmia. The duration of the QRS complex was approximately 50 msec, and its amplitude and shape showed strong spatial variation. Signal-to-noise ratio was inadequate for the study of P and T waves. These data show that this relatively simple and inexpensive instrument can be used for noninvasive in utero investigation of fetal heart activity without requiring a special environment.