MRI of fetus

A fetus in the womb. Credit: Division of Imaging Sciences & Biomedical Engineering, King's College London/CC BY

Biomechanics

Fetal kicks do more than make Mum jump

Movements in utero help to build a strong skeleton.

For the first time, researchers have calculated the forces generated by the movements of human fetuses, and the effects that these forces have on the growing skeleton.

When a fetus kicks and wriggles, its movements place stress and strain on its skeleton. These forces are thought to stimulate healthy development of muscles and bones, but directly measuring their effects has been difficult.

Niamh Nowlan at Imperial College London and her colleagues analysed the kicks of 20- to 35-week old fetuses whose movements had been recorded using an advanced type of magnetic resonance imaging. After creating mathematical models of the uterine wall and the fetuses’ limbs to infer muscle forces and skeletal impacts, the researchers found that kick forces rose between 20 and 30 weeks’ gestation. Later in gestation, kick forces decreased. But stresses and strains on the fetal skeleton were high throughout the second half of pregnancy, the authors say, probably owing to crowding in the womb.