Why do babies
kick in the womb?
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The full narration of the video.
A baby just twenty weeks along, kicking inside the womb, pushes with about as much force as lifting three kilos. So what is all that kicking for? Babies actually start moving at around seven weeks. They're just so tiny then that most mums only feel it between sixteen and twenty-four weeks.
Lots of people think a kick is the baby saying hello, or fussing because something's wrong. But scientists have seen babies keep twitching their arms and legs while they sleep. Kicking in your sleep isn't a message. It's the baby doing two jobs for itself.
Job one: building bones and joints. New bones are still soft in a lot of places. Every kick presses on those spots and nudges them to grow hard and strong. Joints are the same. They have to keep moving to grow into a shape that bends well.
Scientists have seen it in chick and mouse embryos: keep them still, and the joints don't form properly. The bones come out thin and fragile too. Between twenty and thirty weeks, the kicks keep getting stronger. They reach nearly five kilos of force. After that the room gets too cramped, and the kicks actually get weaker. But the push on the bones keeps climbing.
Job two: drawing a map of the body inside the brain. In London, scientists recorded the brainwaves of nineteen newborns. Some were born early and, by the calendar, should still have been in the womb. When a sleeping baby kicked its right leg, the matching little patch on the left side of the brain lit up right away.
Kick, flash. Kick enough times, and the brain learns: this is my leg, and here's where it is. The earlier the baby was born, the stronger the flash. A few weeks after birth, it fades away. So how much a baby moves is an important signal.
Every baby has its own pattern. If a usually busy baby suddenly moves less, don't wait until tomorrow: call your doctor or midwife right away. One mystery is left: does the baby actually mean to kick? The very first moves are probably reflexes. Like when a doctor taps your knee and your leg jumps on its own.
Later the kicks get more organised, probably because the brain takes over. But exactly when it becomes the baby's own choice, scientists still can't say. Got a weird question about the body? Leave it in the comments, and it might be the next episode.
Twenty weeks old,
three-kilo kicks
A baby just twenty weeks along can kick with about as much force as it takes to lift three kilos.
Babies actually start moving at around seven weeks. They are just so tiny that most mums only feel it between sixteen and twenty-four weeks — often after twenty with a first baby. At first it feels like a gentle swirl or flutter; the real kicks come later.
Saying hello?
Or fussing?
But scientists have seen babies keep twitching their arms and legs while they sleep.
Kicking in your sleep isn't a message to anyone. It's the baby doing two jobs for itself.
A little push
hardens soft bone
New bones are still soft in many places (the blue bits in the picture). Every kick presses on those spots and nudges them to grow hard and strong.
Joints are the same: they have to keep moving to grow into a shape that bends well. Scientists have seen it in chick and mouse embryos — keep them still, and the joints don't form properly, and the bones come out thin and fragile.
Each kick is roughly the force of lifting that much. As the room gets cramped, kicks get weaker — but the womb pushes back, so the load on the bones keeps climbing.
Kick once,
the brain flashes
When a sleeping baby kicks its right leg, the matching little patch on the left side of its brain lights up right away.
Scientists in London recorded the brainwaves of nineteen newborns — some born early, who by the calendar should still have been in the womb. Kick, flash. Kick enough times and the brain learns: this is my leg, and here's where it is.
The earlier the baby was born, the stronger the flash. A few weeks after birth it fades away — a lesson taught mostly in the womb.
Moving less?
Don't wait
Every baby has its own pattern. There's no magic number of kicks.
What matters is knowing how your baby usually moves. If a usually busy baby suddenly moves less, or the pattern changes, don't wait until tomorrow — even in the middle of the night, call your doctor or midwife right away.
mean to kick?
