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Image Gallery: Yawning in the Womb

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

24-week old fetus yawning

(Image credit: Nadja Reissland)

Though the exact purpose of yawning is a mystery, 4-D ultrasound images reveal that fetuses yawn in utero

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 is the assistant managing editor and was previously a senior writer for Live Science. Her work has appeared in Scientific American, Wired.com and other outlets. She holds a master's in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's 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.