Fetal Magnetocardiography with an Atomic Magnetometer Array

Fetal magnetocardiography (fMCG) is a powerful technique for analyzing the heartbeat patterns of $\textit{in utero}$ fetuses. We present results from our array of four Spin-Exchange Relaxation-Free (SERF) rubidium-87 atomic magnetometers which has been used to detect and create these magnetocardiograms. We have demonstrated a magnetic noise sensitivity of $<10 \mathrm{fT}/\sqrt{\mathrm{Hz}}$, limited by the Johnson noise of the magnetically-shielded room. We discuss new design features and experimental practices that have increased our sensitivity and allowed us to successfully measure an fMCG at a gestational age of only 21 weeks. We hope to eventually apply these techniques to the detection and diagnosis of heartbeat arrhythmias, which, if detected early enough, can be treated $\textit{in utero}$. This work is supported by the National Institutes of Health.