Supplementary Data for Upload.xlsx from Stresses and strains on the human foetal skeleton during development

Mechanical forces generated by foetal kicks and movements result in stimulation of the foetal skeleton in the form of stress and strain. This stimulation is known to be critical for prenatal musculoskeletal development; indeed, abnormal or absent movements have been implicated in multiple congenital disorders. However, the mechanical stress and strain experienced by the developing human skeleton in utero have never before been characterized. Here, we quantify the biomechanics of foetal movements during the second half of gestation by modelling foetal movements captured using novel cine-MRI technology. By tracking these movements, quantifying foetal kick and muscle forces, and applying them to three-dimensional geometries of the foetal skeleton, we test the hypothesis that stress and strain change over ontogeny. We find that foetal kick force increases significantly from 20 to 30 weeks gestation, before decreasing towards term. However, stress and strain in the foetal skeleton rises significantly over the latter half of gestation. This increasing trend with gestational age is important because changes in foetal movement patterns in late pregnancy have been linked to poor foetal outcomes and musculoskeletal malformations. This research represents the first quantification of kick force and mechanical stress and strain due to foetal movements in the human skeleton in utero, thus advancing our understanding of the biomechanical environment of the uterus. Further, by revealing a potential link between foetal biomechanics and skeletal malformations, our work will stimulate future research in tissue engineering and mechanobiology.