A baby moving in the womb ranks among the most exciting milestones in a pregnancy. Now, researchers at University College London believe they know the reason for this fetal fidgeting.

A baby's movements and kicks while in the uterus might form an essential part of its developing sense of its own body.

That's according to a study of 19 infants published in the journal Scientific Reports.

The neonates were born from six weeks early to a few weeks late. The preterm children stood in for actual unborn fetuses, which would have the same adjusted age.

Lead author Kimberley Whitehead said earlier ultrasound research with fetuses further supports the use of newborns as proxies for late-stage fetuses.

"The movements appear to be similar and comparable when the infant is inside the womb and when they leave the womb," she said.

When newborns in the study moved their right hands, activity increased in the corresponding areas of their brains' left hemispheres. Kimberley Whitehead and her colleagues believe this pattern applies to other bodily movements as well.

The process peters off across the final trimester, and disappears when the baby reaches full term. Whitehead said this supports the idea that womb movement serves a fetal developmental function.

"So around the time they should have been born — so, about 40 weeks — this effect went away, which suggests it might be a mechanism for giving the brain sensory input when a baby would normal still be inside the womb," she said.