Simultaneous registration of uterine contractions and fetal heart rate using magnetomyography and magnetocardiography

Multichannel biomagnetometers allow the acquisition of signals from various sources of physiological electric activity. In this work, we examined magnetic signals simultaneously registered in a pregnant woman originating from the maternal abdomen (magnetomyography MMG) as well as from the fetal heart (fetal magnetocardiography FMCG). Using a 61 channel biomagnetometer which covered the complete maternal abdomen, we recorded MMG and FMCG for 15 min at a sampling rate of 1 kHz and a bandpass of 1-200 Hz. During this period the mother experienced several episodes of contractions. Appropriate signal processing such as filtering, template matching and digital subtraction / averaging of signal components permitted the identification of signals associated with both uterine contractions as well as with fetal cardiac activity. Data analysis showed that broad band high frequency signals related to the contractions were consistently associated with rapid sustained increases in fetal heart rate and decreases in short-term heart rate variability. We conclude that MMG may identify episodes of uterine contraction and that their effect on fetal heart rate can be assessed simultaneously on the basis of FMCG. This combination of MMG and FMCG may thus aid in fetal monitoring.