Ahh, the life of a growing baby—so tiring! New 4D scans of 15 fetuses found that fetuses do actually yawn while in the womb, ScienceDaily reports. But it's actually not because they're tired, the lead researcher says; rather, "the frequency of yawning in the womb may be linked to the maturing of the brain early in gestation." Yawning was seen to decline in fetuses after 28 weeks gestation.
Researchers think yawning could be a developmental marker and could help doctors to assess the health of a fetus. Scientists have disagreed in the past over whether fetuses actually yawn or simply open their mouths, but this research distinguished between yawning and other, non-yawn mouth openings based on how long the mouth remained open. More than half of all mouth openings observed by researchers were determined to be yawns. (And no: Fetus yawns were not found to be "contagious." Babies are also immune to "contagious" yawning.)