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Fetal heart rate variability was derived from fetal magnetocardiogram recordings in ten subjects at gestation ages 32–38 weeks. Maternal interference was negligible and R-wave detection was highly reliable. Oscillations suggestive of respiratory sinus arrhythmia (RSA) were prominent in many of the heart rate tracings. Spectral analysis was used to quantify heart rate variability and to examine the influence of the RSA-like oscillations on heart rate variability. The oscillations were associated with increased power in the frequency range 0.4–1.0 Hz (P ≤ 0.05). Magnetic recording appears to offer significant advantages for investigation of beat-to-beat fetal heart rate throughout the latter stages of pregnancy.

Fetal cardiac waveform intervals were assessed from fetal magnetocardiogram (FMCG) recordings taken from 59 pregnant women at 17-41 weeks gestation. Beyond 27 weeks' gestation PR and QRS intervals, measured from averaged waveforms, could be obtained from all subjects; however, prior to 21 weeks' gestation the success rate was 50% or less due to low signal-to-noise ratio. QT interval could not be assessed accurately in most subjects. Weak, but statistically significant, correlations with gestational age were found for PR interval (n = 145, R2 = 0.033, P = 0.028) and QRS interval (n = 145, R2 = 0.140, P < 0.0005). Abnormal waveform morphology was documented in several patients with cardiac malformations.