Carlos Solis
Yawning isn’t just human — it shows up across mammals, which suggests it serves an important brain function. A study from the University of Parma adds a surprising twist: the contagion effect may begin before birth.
A fetus begins to yawn fairly early — around week 11 of pregnancy. Until now, researchers didn’t know whether those yawns follow the fetus’s own schedule or can sync with the mother’s yawns.
The study involved 38 women, ages 18 to 45, each with an uncomplicated pregnancy in the third trimester (28–32 weeks).
How the experiment worked
Pregnant participants sat in silence in front of a screen while researchers video-recorded their faces and monitored the fetuses with ultrasound. First they showed one minute of a neutral landscape to establish a baseline of quiet behavior. Then they ran three six-minute video sessions:
- videos of people yawning;
- videos of people opening and closing their mouths in a movement similar to, but not identical to, yawning;
- videos of neutral faces.
Most women yawned while watching the yawning videos. More striking, their fetuses joined in too. In about half the cases, mother and fetus yawned in sync.
What this might mean
The team concludes that yawning contagion runs deeper than we thought — it may begin in the womb. They also flag key limitations: the sample is small, all participants came from a single Italian maternity ward, and the study covers only a narrow pregnancy window (28–32 weeks). We still don’t know exactly when this synchronization starts during pregnancy or whether it appears consistently across populations.
The study doesn’t identify a physiological pathway that would explain how a mother’s yawning affects fetal behavior. That brings us back to a bigger question: why do we yawn at all?
The strongest current hypothesis says yawning helps cool the brain. Recent neuroimaging suggests other functions as well. And we still don’t fully understand why yawning is so contagious.
“Most likely, these results fit a form of prenatal physiological synchronization between mother and fetus,” D’Adamo writes. “Contact yawning can be understood as a socially engaged expression of a motor pattern that already exists and is available at early stages of development.”
The article appears in the journal Current Biology
