Fetal magnetocardiography: Using quantum technologies to define fetal rhythm, conduction, and repolarization prior to birth.

The timeframe of fetal development holds many risks, and mortality is higher than at almost any other time in the human life-cycle. To date, echocardiography has dominated fetal cardiac assessment. Since the 1990's, the potential value of fetal magnetocardiography (fMCG) as a means of recording the fetal rhythm and cardiac time intervals (RR, P, PR, QRS, QT, QTc) has been appreciated. Over the intervening 3 decades, well over 1000 fetal studies have been performed in pregnancies with various high-risk conditions, the majority with fetal arrhythmias or congenital heart disease. Most studies to date have been performed using Superconducting Quantum Interference Device (SQIUD) magnetometers within a magnetically-shielded room (MSR). Since 2015, a new type of quantum device called an Optically-pumped magnetometer (OPM) has been introduced. These small sensors can be assembled for multichannel recording. OPMs do not require cryogenics, dramatically reducing the potential cost of a system, and thus allowing for the concept of a "person-sized shield rather than a full-sized MSR. Yet no OPM systems are yet FDA approved for the fetus. This contemporary review will summarize the current and future use of fMCG in the clinical and research setting and will compare fetal MCG by OPM with that of SQUID. Challenges to commercialization will be discussed.