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Spectral analysis of heart rate has shown that changes in the power of frequency bands below 1 Hz reflect physiological changes associated with the autonomic nervous system (ANS) [1]. In particular the low frequency band (LF) between 0.04 and 0.15 Hz is often associated with sympathetic as well as parasympathetic activity, whereas the high frequency band (HF) in the range from 0.15 to 0.4 Hz is mediated by parasympathetic activity. An overall index of sympathovagal balance in the control of the heart rate is given by the ratio LF/HF. Furthermore, in adults the HF peak reflects the modulation of heart rate due to respiration known as respiratory sinus arrhythmia (RSA).

The frequency of multiple pregnancies, twins as well as higher grade, is increasing, among other things, due to fertilizing therapy. Such pregnancies are known to be of elevated risk for mother and child and, as a consequence, a more intensive surveillance is required. It has been shown that fetal magnetocardiography (FMCG) is a facile method of registering fetal cardiac activity Crom the second trimester onward [1,2]. We would like to present the possibility of using the fetal magnetocardiogram as an adjunct to Standard diagnostic tools in twin pregnancy.

Several studies have indicated that fetal cardiac time intervals (CTI) derived from the electric or magnetic cardiac signal increase in the course of pregnancy [1–3]. Such changes can be related to the size, development and maturity of the fetal heart and may thus serve as a measure reflecting not only normal cardiac function, but also the intrauterine growth state of the fetus as a whole. Another parameter which can be determined from the fetal cardiac signal is the amplitude of the signal at depolarisation and repolarisation times. In particular, the ratio of the T wave amplitude to the QRS complex amplitude (T/QRS) has been shown to increase in response to hypoxia during labor [4]. Little is known about changes in such amplitudes in the course of pregnancy. Among other things, this is due to the difficulty in obtaining viable electrocardiographic (ECG) signals consistently at different gestational ages (GA). ECG examination of the fetal cardiac signal is limited by noise, maternal artifacts and the insulating effects of the vernix caseosa. In this respect, fetal magnetocardiography (FMCG) has been shown to be a simple, noninvasive, and effective method in fetal monitoring, registering high quality fetal cardiac activity anytime during the pregnancy from the second trimester onwaid. The acquisition of the fetal cardiac magnetic signal enables the analysis of signal morphology for the complete beat with great accuracy [2]. The purpose of this study was to register fetal cardiac activity at regular intervals in the course of healthy pregnancies with magnetocardiography in order to determine fetal CTI and signal amplitudes accurately and to investigate the changes of these parameters over time.

Heart rate variability (HRV) is an important marker for fetal well-being. Various methods have been used to analyse HRV, in particular parameters from the time and frequency domain [1]. Recently mathematical methods have been introduced which go beyond the examination of overall variance or rhythmic changes in heart rate [2,3]. The goal is to quantify temporal complexity by examining the chaoticity of time series in a reconstructed State space. These methods can be applied to fetal heart period time series to examine whether irregular but typical nonlinear dynamical heart rate patterns can be identified. These patterns might then be linked to fetal well-being.