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Fetal magnetocardiography (fMCG) has been shown to augment fetal ultrasound evaluation for high-risk conditions, but the clinical utility of fMCG depends on the reliability of the cardiac traces reconstructed. We performed a methodological study to examine the influence of gestational age on the properties of the fetal magnetocardiograms extracted with two methods of signal reconstruction: the template matching technique (TMT), which extracts the maternal components from the signal using only temporal information, and independent component analysis (ICA), which separates the fetal signals by using information on the spatial distribution of the mixed source signals in addition to higher order temporal statistics. Efficiency and accuracy were evaluated in terms of fetal beat detection, signal characteristics, and duration of cardiac time intervals (CTIs) on the averaged traces. ICA outperformed TMT with regard to beat detection and signal-to-noise ratio. The timing of the heartbeats and the duration of the CTIs were essentially the same, whereas some alterations in signal morphology were observed in the ICA traces. We conclude that ICA may be useful in early gestation when the signals are noisy, while TMT may be preferred when accurate beat morphology is required for diagnostic purposes.

From adult data, it is known that numerous factors, such as age, state of the autonomic nervous system, diurnal rhythms or mean R-R interval mRR, influence heart rate variability (HRV). The aim of this study was the examination of the influence of gestational age, mRR, gender and time of day on fetal HRV. The analysis was based on 66 fetal magnetocardiograms (FMCGs) of 22 healthy fetuses between the 16th and 42nd week. FMCGs were recorded for 5 min using a multichannel biomagnetometer. On the basis of the time series of fetal R-R intervals, mRR as well as the standard deviation sdRR, root mean square of successive differences rmssdRR and approximate entropy ApEn were calculated. The influence of gestational age, mRR and gender on sdRR, rmssdRR and ApEn was determined by regression analysis. The relationship between time of day and HRV was evaluated by visual inspection of scatterplots. The logarithmised HRV measures increased significantly with the logarithm of gestational age (regression coefficients: sdRR = 1.28, rmssdRR = 1.12, ApEn = 1.30) and mRR (regression coefficients: sdRR = 0.008, rmssdRR = 0.011, ApEn = 0.012) There was no significant influence of gender. With respect to time of day (between 0800 h and 1800 h), no dependency of the HRV measures was apparent. In summary, when fetal HRV is assessed, it is essential to take gestational age and mRR into account. In contrast, time of day, with respect to daytime, and gender need not be considered. In future studies, the influence of fetal activity state on HRV should be examined.

Abstract.: Aim of this work was to compare fetal cardiac time intervals (CTI) in twin and singleton pregnancies taking gestational age into account. Eighteen fetal magnetocardiograms were obtained in 14 twin fetuses (28th–38th week of gestation). In the signal averaged fetal PQRST courses, the following CTI were determined: P wave, PR interval, PQ interval and QRS complex. The CTI of 228 magnetocardiograms from 47 singleton fetuses served as controls. The CTI of both groups were compared using a regression model including gestational age and singleton/twin status. Atrioventricular conduction and ventricular depolarization times could be determined reliably. Regression analysis showed that P, PQ and PR duration were significantly shorter in the twin fetuses than in the control group (3.7 ms, p =0.020; 6.5 ms, p =0.050; 10.2 ms, p =0.004; respectively). No difference in QRS duration was found. Values for birth weight, length and head circumference were significantly lower in the twin fetuses. The results show that, in twin pregnancy, reduced fetal size and weight may be reflected in shorter CTI, in particular those associated with atrioventricular conduction. The values obtained here are however not as low as those in previously published values found in growth retarded fetuses. [Copyright &y& Elsevier]