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Fetal magnetocardiography: time intervals and heart rate variability.

Biomagnetism in the perinatal domain has been dominated by fetal cardiology, and early work pointed out the potential of both fetal cardiac time intervals (CTI) and heart rate variability (HRV) for future clinical applications. Recent improvements in instrumentation have permitted numerous groups to investigate a substantial number of healthy fetuses in these two areas and to lay the groundwork for a delineation of normal ranges. With respect to fetal CTI it is now clear that in particular the duration of P wave, PR interval and QRS complex reflect fetal growth and development. Preliminary studies have shown that the age-adjusted CTI are shorter in growth-retarded fetuses and altered in cases of structural cardiac defects and in specific types of arrhythmia. Less work has been published on MCG-determined fetal HRV although parameters from both the time and frequency domains as well as complexity have been examined. Concomitant with the gradual change in heart rate during pregnancy, increases in time domain variables and complexity have been described for normal pregnancies. Furthermore, gestational age-related changes in specific spectral bands have been noted and increases in power have been documented at frequencies which are associated with fetal breathing movements. The fact that little has been reported to date on discriminatory power with respect to pathological states may be due to the lack of extended data acquisition in a clinical setting documenting acute states. Nonetheless, it may be expected that both fetal HRV and CTI will supplement standard fetal surveillance techniques in the near future.