Supplementary Material for: Cross-sectional Observational Study of Typical in-utero Fetal Movements using Machine Learning

Early variations of fetal movements are the hallmark of a healthy developing central nervous system. However, there are no automatic methods to quantify the complex 3D motion of the developing fetus in-utero. The aim of this prospective study was to use machine learning (ML) on in-utero MRI to perform quantitative kinematic analysis of fetal limb movement, assessing the impact of maternal, placental, and fetal factors. In this cross-sectional, observational study, we used 76 sets of fetal (24-40 gestational weeks (GW)) blood oxygenation level-dependent (BOLD) MRI scans of 52 women (18-45 years old) during typical pregnancies. Pregnant women were scanned for 5 to 10 minutes while breathing room air (21% O2) and for 5 to 10 minutes while breathing 100% FiO2 in supine and/or lateral position. BOLD acquisition time was 20 minutes in total with an effective temporal resolution of approximately 3 seconds. To quantify upper and lower limb kinematics, we used a 3D convolutional neural network (CNN) previously trained to track fetal key points (wrists, elbows, shoulders, ankles, knees, hips) on similar BOLD time series. Tracking was visually assessed, errors manually corrected and the absolute movement time (AMT) for each joint was calculated. To identify variables that had a significant association with AMT, we constructed a mixed-model ANOVA with interaction terms. Fetuses showed significantly longer duration of limb movements during maternal hyperoxia. We also found a significant centrifugal increase of AMT across limbs and significantly longer AMT of upper extremities 35 GW. In conclusion, using ML we successfully quantified complex 3D fetal limb motion in-utero and across gestation, showing maternal factors (hyperoxia) and fetal factors (gestational age, joint) impact movement. Quantification of fetal motion on MRI is a potential new biomarker of fetal health and neuromuscular development