胎兒在子宮中踢腿是因爲他也需要運動!

The first time a pregnant woman feels her baby kick can be surprising -- a sudden reminder that the tiny creature growing inside her has a mind of its own. But why do babies kick?

孕婦第一次感受到胎兒踢腿可能會覺得很驚奇--這是突然提醒她，在她體內生長的小生命開始有自己的想法了。但爲什麼胎兒會踢腿呢？

Though the womb is a tight space in which to exercise, it turns out that those kicks are vital for the baby's healthy bone and joint development, an expert told Live Science.

一名專家向《生活科學》透露，儘管子宮是一個擁擠的運動場所，但這些踢腿動作對胎兒骨骼健康和關節發育至關重要。

Fetuses begin moving in the womb about as early as 7 weeks, when they slowly bend their necks, according to a review paper published in the journal Ultrasound in Obstetrics & Gynecology.

發表在《婦產科超聲》雜誌上的一篇評論文章指出，胎兒最早在7周時就能在子宮中運動，那時他們會慢慢地彎曲脖子。

As the babies grow, they gradually add more movements to their repertoire, such as hiccupping, arm and leg movements, stretching, yawning, and thumb sucking.

隨着胎兒的生長，他們的動作會逐漸增多，例如打嗝、動胳膊動腿、伸展、打哈欠和吮吸拇指。

But the mom won't feel the bigger movements -- such as kicks and punches -- until 16 to 18 weeks into her pregnancy, when the baby is a bit stronger.

但孕婦只有到懷孕16周至18周時才能感受到幅度較大的動作，例如踢腿和擊打，此時胎兒已經更強壯了。

An entire field of research is dedicated to figuring out whether the baby is in control of its movement or if those movements are just a reflex, said Niamh Nowlan, a bioengineer at Imperial College London.

倫敦帝國理工學院生物工程學家尼婭姆·諾蘭稱，一個完整的研究正在致力於弄清楚是胎兒能控制這些動作，還是說這些動作只是一種反射。

"Early movements are likely to be purely reflex," Nowlan told Live Science in an email, "but as the movements become more coordinated, it's likely the brain is in control of how much and when the baby moves."

諾蘭在發給《生活科學》的一封電子郵件中寫道：“早期的動作很可能只是純粹的反射，但隨着動作變得更加協調，很可能是大腦在控制胎兒的運動速度和時間。”

Scientists may not know for sure if the movements are voluntary or involuntary, but Nowlan said the research is clear that movement is important.

科學家們或許無法確定胎兒是主動還是無意識做出這些動作的，但諾蘭說，研究明確了一點：運動很重要。

"The baby needs to move in the womb to be healthy after birth, particularly for their bones and joints," she said.

她說：“胎兒需要在子宮裏運動以保持健康，尤其是對他們的骨骼和關節而言。”

In a review she published in the journal European Cells and Materials, Nowlan described how a lack of fetal movement can lead to a variety of congenital disorders, such as shortened joints and thin bones that are susceptible to fracture.

諾蘭在期刊《歐洲細胞和材料》上發表的一篇評論性文章描述了缺乏胎動是如何導致各種先天疾病的，例如關節短和骨骼細，這些問題容易引發骨折。

For pregnant women wondering if their baby is too kicky, or not kicky enough, Nowlan said there's no established amount of normal fetal movement during pregnancy. "Pregnant women are told to look out for significant changes in movements, which is quite vague advice, but it's the best that can be given at the moment," she said.

對於那些擔心寶寶胎動太多或是太少的孕婦，諾蘭表示，在孕期胎兒運動並沒有固定的量。她說：“孕婦被告知要注意胎動的明顯變化，這是一個非常模糊的建議，但也是當前能提供的最好的建議。”

That's because it's difficult for scientists to study fetal movements, because the only way to measure them is in the hospital and it can be done for only a short period at a time. It's unlikely that each woman will feel the same thing when her baby starts kicking.

這是因爲科學家很難研究胎兒的運動，要監測它們的唯一方式就是在醫院裏，而且只能在短時間內完成。當胎兒開始踢腿時，每個準媽媽的感覺可能不同。

"Different women experience the sensation quite differently, and sensations can vary between pregnancies," Nowlan said.

諾蘭說道：“不同的女性對這種感覺的感受是完全不同的，而且同一個人每次懷孕期間的感覺也會有所不同。”

Feeling a baby moving and kicking in the womb might be a weird sensation, but it's simply a sign of healthy development.

感受胎兒在子宮中動動和踢腿或許是種怪怪的體驗，但這其實不過是健康發育的跡象。