The precise reasons why we yawn have puzzled scientists since they first started thinking about this contagious, slow-motion, mouth-opening motion. And now there’s a new wrinkle in the conundrum. Researchers have discovered that fetuses yawn in the womb.
Using ultrasound video recordings, researchers have worked out a technique to distinguish prenatal yawns from simple mouth openings.
In the study, scientists scanned 15 healthy fetuses, eight girls and seven boys, at 24, 28, 32 and 36 weeks’ gestation. By timing the actions and analyzing the shapes of the fetuses’ mouths, the scientists were able to distinguish yawns from random jaw openings. In all, they counted 56 yawns and 27 non-yawn oral openings. They also discovered that the yawning stopped at 36 weeks.
Though the researchers believe that fetus and adult yawns occur for different reasons, it remains unclear what the reasons are in either case.
“When you see a fetus yawning, it’s not because it’s tired,” says the study’s lead author, Nadja Reissland, a developmental psychologist at Durham University in England. “The yawning itself might have some kind of function in healthy development. Fetuses yawn, and then as they develop they stop yawning. There’s something special in yawning.”