PARENTS
03/16/2018 14:25 EDT | Updated 03/16/2018 14:25 EDT

There's A Scientific Reason Babies Kick So Much In The Womb

They're not just saying "oh, HI."

The first time you feel your baby kick is usually a cause for celebration.

Then those little flutters turn into hard jabs to the bladder, and what was once cute is now causing you to pee your pants in the grocery store. Still, especially in the earlier days of pregnancy, the movements are a reminder that your swollen belly isn't just a result of those lunchtime tacos, but that there's an actual baby in there. And that's exciting (when baby isn't practicing her soccer moves at 4 a.m.)

Now it turns out there's a scientific reason babies kick in the womb. (And here we thought they were just saying "hi.")

A new study published March 12 in Development found that babies move around so much in the womb because it's how they develop strong bones and cartilage. The researchers, who looked at chick and mouse embryos, discovered that there are "some key molecular interactions that are stimulated by movement and which guide the cells and tissues of the embryo to build a functionally robust yet malleable skeleton," according to a press release from Trinity College Dublin.

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Movements in the womb help babies develop strong bones and joints.

An embryo who doesn't move is at risk for developing brittle bones or abnormal joints, the press release noted.

"The relative lack of understanding around how cartilage was directed presented an unfortunate knowledge gap because there are many painful, debilitating diseases that affect joints — like osteoarthritis — and because we also often injure our joints, which leads to them losing this protective cartilage cover," co-author Paula Murphy, professor in zoology at Trinity College Dublin, said in the release.

"Our new findings show that in the absence of embryonic movement the cells that should form articular cartilage receive incorrect molecular signals, where one type of signal is lost while another inappropriate signal is activated in its place. In short, the cells receive the signal that says 'make bone' when they should receive the signal that says 'make cartilage.'"

So, basically, those kicks and rolls you feel are actually your baby forming his or her little body. Which is kind of wild.

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You might start noticing kicks around 18-20 weeks.

You might start noticing that your baby moves and kicks more at certain times of day starting around 18-20 weeks, according to HealthLink B.C. You might feel more kicks when you're resting than when you're active, they added.

Sometimes, in the last trimester of pregnancy, your doctor may ask you to keep track of your baby's kicks and movements, HealthLink B.C. said.

"Six movements (such as kicks, flutters, or rolls) in two hours or less are considered normal. But do not panic if you do not feel six movements. Less activity may simply mean the baby is sleeping."