Image Gallery: Yawning in the Womb

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Ultrasound videos have captured fetuses yawning in the womb. (Image credit: Nadja Reissland)

24-week old fetus yawning

(Image credit: Nadja Reissland)

27-week old fetus

(Image credit: Nadja Reissland)

Yawns can be distinguished from feeding reflexes because yawning mouths spend longer open and have a shorter closing period.

28-week old fetus

(Image credit: Nadja Reissland)

As babies mature, they yawn less frequently. Researchers believe yawning may help trigger brain development.

32-week old fetus

(Image credit: Nadja Reissland)

Because yawning frequency changes throughout pregnancy, yawn patterns could be used as a marker of healthy development.

Yawning in utero

(Image credit: Wolfgang Moroder)

By the time babies are full-term, they have stopped yawning in the womb.

Fetal Faces

Fetal facial expressions develop in the womb

(Image credit: Nadja Reissland)

Researchers used ultrasound images of fetuses' faces, like these, to track how they used progressively more complex facial movements.

Tia Ghose
Tia Ghose
Editor-in-Chief (Premium)

Tia is the editor-in-chief (premium) and was formerly managing editor and senior writer for Live Science. Her work has appeared in Scientific American, Wired.com, Science News and other outlets. She holds a master's degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.