Influence of Maternal and Fetal Factors on Fetal Magnetocardiography Measurements Using Optically Pumped Magnetometers

Background Fetal magnetocardiography (fMCG) noninvasively measures the magnetic fields generated by the fetal heart to assess cardiac electrophysiology. The advent of optically pumped magnetometers (OPMs) enables portable, cryogen-free acquisition of high-fidelity fMCG signals. However, maternal and fetal characteristics may introduce variability affecting signal quality and cardiac time-interval (CTI) detectability. Objective This study quantifies the influence of maternal and fetal parameters (placental position, body mass index (BMI), fetal heart distance, and gestational age (GA)) on the signal-to-noise ratio (SNR) and CTI detectability in OPM-based fMCG recordings. Methods A total of 107 OPM recordings were obtained longitudinally from 32 pregnant participants (28-38 weeks of gestation) using a bed-based, stand-alone OPM array system. SNR was derived from fMCG signals, and maternal and fetal characteristics were obtained from clinical data. Mixed-effects linear and logistic regression models were used to evaluate associations between these parameters, SNR and CTI detectability. Results Mean SNR and variance were 10.95 dB and 14.56 dB 2 , respectively. Multivariable mixed-effects linear regression reduced total variance to 12.55 dB 2 and yielded a fixed-effects R 2 of 19.8%. SNR increased significantly with GA and decreased with fetal heart distance. Higher SNR was associated with improved CTI detectability, particularly for T wave and QT interval. GA remained a significant predictor of T-wave detectability, while fetal heart distance exerted an independent negative effect. Conclusion Fetal heart distance and GA are the primary determinants of OPM-fMCG signal quality. Accounting for maternal physiological variability is essential for optimizing acquisition protocols and improving the interpretability of fetal cardiac data.