Cardiac vectors in the healthy human fetus: developmental changes assessed by magnetocardiography and realistic approximations of the volume conductor.

This study sought to characterize the developmental changes of three measures used to describe the morphology of the fetal cardiac vector: QRS peak-amplitude, QRS duration and QRS time-amplitude integral. To achieve this objective, we rely on a recently developed methodology for fetal cardiac vector estimation, using multichannel fetal magnetocardiographic (fMCG) recordings and realistic approximations of the volume conductors obtained from free-hand ultrasound imaging. fMCG recordings and 3D ultrasound images were obtained from 23 healthy, uncomplicated pregnancies for a total of 77 recordings performed at gestational ages between 22 and 37 weeks. We report the developmental changes of the cardiac vector parameters with respect to gestational age and estimated fetal weight, as well as their dependence on the estimated ventricular mass derived from cardiac dimensions measured with M-mode ultrasound. The normative values can be used along with the cardiac time intervals reported by previous fMCG studies to assist future clinical studies investigating conditions that affect fetal cardiac function.

Non-nutritive sucking recorded in utero via fetal magnetography.

Several studies in term and pre-term infants have investigated the rhythmic pattern of non-nutritive sucking (NNS) indicating correlations between the quantitative measures derived from sucking pressure variation and/or electromyographic (EMG) recordings and a range of factors that include age, perinatal stress and sequelae. In the human fetus, NNS has been reported from 13 weeks of gestation and has been studied using real-time Doppler ultrasonography exclusively. The present study indicates that NNS in fetus can be reliably recorded and quantified using non-invasive biomagnetic measurements that have been recently introduced as an investigational tool for the assessment of fetal neurophysiologic development. We show that source separation techniques, such as independent component analysis, applied to the high-resolution multichannel recordings allow the segregation of an explicit waveform that represents the biomagnetic equivalent of the ororhythmic sucking pressure variation or EMG signal recorded in infants. This enables the morphological study of NNS patterning over different temporal scales, from the global quantitative measures to the within burst fine structure characterization, in correlation with the fetal cardiac rhythm.

Magnetographic assessment of fetal hiccups and their effect on fetal heart rhythm.

Fetal hiccups emerge as early as nine weeks post-conception, being the predominant diaphragmatic movement before 26 weeks of gestation. They are considered as a programmed isometric inspiratory muscle exercise of the fetus in preparation for the post-natal respiratory function, or a manifestation of a reflex circuitry underlying the development of suckling and gasping patterns. The present paper provides the first evidence of non-invasive biomagnetic measurements of the diaphragm spasmodic contractions associated with fetal hiccups. The magnetic field patterns generated by fetal hiccups exhibit well-defined morphological features, consisting of an initial high frequency transient waveform followed by a more prolonged low frequency component. This pattern is consistent across recordings obtained from two fetal subjects, and it is confirmed by signals recorded in a neonatal subject. These results demonstrate that fetal biomagnetometry can provide insights into the electrophysiological mechanisms of diaphragm motor function in the fetus. Additionally, we study the correlation between hiccup events and fetal cardiac rhythm and provide evidence that hiccups may modulate the fetal heart rate during the last trimester of pregnancy.