Yawning is contagious, and a new study suggests the phenomenon may begin before we are even born.
Researchers at the University of Parma in Italy observed 38 women in their third trimester. The mothers watched videos of people yawning while ultrasound monitored their fetuses. When a mother yawned while watching the footage, her fetus was likely to yawn too.
The study, published in Current Biology, reports a robust positive association between maternal and fetal yawning frequencies. The synchronization occurred in half of the cases during yawning videos, but not during control videos.
The findings challenge previous assumptions that fetal yawning is purely independent. Instead, the authors suggest this may be a form of intrauterine physiological contagion.
The exact mechanism remains unknown, as does the primary function of yawning itself. The leading hypothesis is brain cooling. Researchers call for larger, more diverse studies.