Babies in the Womb Pack a Powerful Kick

The team used MRI scans of babies moving inside of their mothers. Imperial College London

Even while still in their moms' bellies, developing babies can pack a powerful punch, or kick that is. New research from London has calculated for the first time just how powerful fetuses are, and found that their tiny legs can kick their mothers' wombs with upwards of 10 pounds of force.

The study now published online in the Journal of the Royal Society of Interface studied the mechanical forces generated by a fetus's kick to better understand not only the strength of the developing baby, but also how this strength affects the baby's developing skeletal systems (not to mention strains the mother's uterine walls). The study is the first to explore fetus kick force and the mechanical stress and strain due to fetal movements in the human skeleton in utero.

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For the study, the team of researchers from Imperial College London used MRI scans to look at fetuses in their mothers' wombs. Then they built computer models based on the scans to track the movements of the fetuses' joints. These measurements were used to calculate both the strength of the fetuses' kick and the stress it placed on the bones, Live Science reported.

Results revealed the in-utero kicks were shockingly strong, and went from about 6.5 to 10.5 pounds of force between 20 and 30 weeks of gestation. However, as the fetus continues to grow it has less room to kick, and as a result, the kicks become less powerful. By the 35th week of gestation, a fetus' kicks are only about 3.8 pounds of force.

The study helps us better understand how babies move while still developing. Imperial College London

A pound force is a measurement of force commonly used in mechanical engineering. It is defined as the forced required to accelerate a mass.

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Although fetuses can start moving as early as seven to eight weeks in the pregnancy, according to Baby Center, mothers usually don't start to feel the baby kick until around 16 and 22 weeks.


While stress on the bones may sounds negative, according to the study, it can have positive effects on the developing baby. The stress of these powerful kicks helps to strengthen a fetus's developing bones and joints. The study notes that this makes sense as changes in fetal movement patterns in late pregnancy are linked to poor outcomes and musculoskeletal malformations.