Determination of Changes in Fetal Cardiac Time Intervals and T/QRS Ratio During Pregnancy Using Magnetocardiography
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 . 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 . The purpose of this study was to register fetal cardiac activity at regulär 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.
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