Fetuses sometimes yawn when their mothers do, even without being able to see their faces
A fetus doesn’t need to see a yawn to catch it.
Mothers can make their unborn offspring yawn during pregnancy, researchers report May 5 Current biology.
Yawning is contagious among many social creaturesincluding humans, dogs, lions and parakeets. Although this behavior is commonly thought to stimulate blood flow to the brain for cooling and alertness, yawning might also help. synchronize group movements and be a primitive form of empathy. And yawning begins even before birth. Yawning in utero supports brain development, ensuring that all the muscles and brain connections needed for yawning and breathing are in good working order.
But researchers largely attribute these prenatal yawns to natural bodily programming, different from the socially contagious reflex that affects both children and adults. It was not known whether the mother’s yawning had an impact on the fetuses.
Pregnancy is a time when mothers and their fetuses are inextricably linked not only physiologically, but perhaps behaviorally, says Giulia D’Adamo, a neuroscientist and psychologist at the University of Parma in Italy. “During pregnancy, everything is the basis for what will happen next.”
To test whether fetuses pick up on their mothers’ yawns, D’Adamo and colleagues showed videos of people yawning to a group of 38 pregnant women who were in their third trimester. The cameras captured the mothers’ video yawns while ultrasound monitored their fetuses.
About 64% of mothers yawned at least once in response to the video. Just over half of the fetuses responded to their mothers, yawning about a minute and a half later. (The upper limit for “catching” a yawn in humans is about five minutes.) This fetal yawn was much more likely to follow a maternal yawn than to occur spontaneously.
It’s possible that the physical movement of a yawn puts pressure on the uterus in a way that signals to the fetus that it should yawn too, D’Adamo says. Hormones could also cause fetal yawning. Future studies examining women at different stages of pregnancy could help uncover how mothers convey their yawns.
But for now, we don’t know why fetuses yawn and whether these yawns benefit their future behaviors. The real social context, D’Adamo says, occurs after birth.