Assessment of fetal autonomic nervous system activity by fetal magnetocardiography: Comparison of normal pregnancy and intrauterine growth restriction

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Aim : To clarify the developmental activity of the autonomic nervous system (ANS) of the normal fetus and to compare developmental activity between normal pregnancy and the case of intrauterine growth restriction (IUGR) using fetal magnetocardiography (FMCG).Methods : Subjects consisted of normal pregnancy (n = 35) and IUGR (n = 12) cases at 28-39 and 32-37 weeks gestation, respectively. FMCG was recorded using 64-channel magnetocardiography (MCG) in a magnetically shielded room. The QRS interval was derived from signal-averaged MCG; the R由 interval variability induced by an R-wave trigger was eventually adopted to calculate the coefficient of variance (CVRR) and low frequency/high frequency (LF/HF) ratio.Results : The value of CVRR in the normal pregnancy group displayed a slight increasing trend with gestational age (y = 1.77 + 0.10x ; r = 0.32) ; however, no such trend was observed in the IUGR group. In contrast, the LF/HF ratio in the normal pregnancy group clearly increased over the gestational period (one-way ANOVA: P = 0.003). The LF/HF ratio in the IUGR group also displayed an increasing trend over the gestational period (y = 2.47 + 0.05x ; r = 0.05).Conclusions : Analyses based on the time and frequency domains of heart rate variability using FMCG enable the evaluation of fetal ANS activity. Sympathetic nervous activity increased with gestational age in the normal pregnancy group ; however, the development of fetal ANS activity in IUGR cases might differ from that observed in the normal pregnancy group.