Babies May Catch Yawns Even Before Birth, Study Suggests

A new study has found that contagious yawning may begin in the womb, as fetuses can "catch" yawns from their mothers as early as the second trimester. The findings, published in Current Biology, add a prenatal twist to one of the most studied and still mysterious social behaviours, that is, yawning and its chain reaction.

Researchers at the University of Parma recruited women with healthy, uncomplicated pregnancies. Each mother watched a series of videos: some showing people yawning, some showing people opening and closing their mouths, and some showing still faces.

A camera recorded the mother's face, while a 2D ultrasound machine monitored the fetus's nose and lips in real time. As expected, about 64% of the mothers yawned at least once while viewing yawning videos, and almost no one yawned during the other clips.

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But the surprise was in utero as around 53% of fetuses yawned when their mothers watched yawning videos. The fetal response typically occurred roughly one and a half minutes after their moms yawned.

As per the authors, "mothers who yawned more also tended to have fetuses that yawned more, revealing a robust positive association between maternal and fetal yawning frequencies."

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Scientists don't fully understand the mechanism, but they have a few hypotheses. "Rather, they are more consistent with a form of intrauterine physiological contagion, likely grounded in the bodily and interoceptive consequences of maternal actions," the authors write.

"Contagious yawning may be understood as the socially recruited expression of a motor pattern that is already robust and available early in development."