Fetuses Yawn in Response to Mothers' Yawns, Study Finds

Fetuses can catch yawns from their mothers during pregnancy without seeing them, researchers reported in a study published on May 5 in Current Biology. Giulia D’Adamo, a neuroscientist and psychologist at the University of Parma in Italy, and her colleagues showed videos of yawning people to 38 pregnant women in their third trimester.

Cameras captured the mothers’ video-prompted yawns while ultrasound monitored their fetuses.

Roughly 64 percent of the mothers yawned at least once in response to the video. Just over half of the fetuses responded to their mothers by yawning themselves around a minute and a half later. The upper limit to catching a yawn for humans is around five minutes.

Yawning is contagious among humans, dogs, lions and parakeets. Yawning begins even before birth, and in utero yawns support brain development.

Researchers had largely attributed these prenatal yawns to natural body programming, different from the socially contagious reflex seen in children and adults. It was previously unknown whether a mother’s yawning had any impact on fetuses. “During pregnancy, everything is groundwork for what is going to happen next,” D’Adamo said.

Hormones could also prompt a fetal yawn. Future studies examining women at various stages of pregnancy could help uncover how mothers pass on their yawns.

For now it remains unclear why fetuses catch yawns and whether those yawns serve to benefit any future behaviors.