Spectral analysis of antepartum fetal heart rate variability from fetal magnetocardiogram recordings

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 < or = 0.05). Magnetic recording appears to offer significant advantages for investigation of beat-to-beat fetal heart rate throughout the latter stages of pregnancy.