Scientists in England have confirmed unborn babies do yawn while inside their mother's womb.
Ultrasound footage of foetuses appearing to yawn in utero has been posted online by excited parents and this inspired researchers at the University of Durham to determine whether the infants were yawning or just opening their mouths.
"Fetus yawning is not contagious, nor do they yawn because they are 'sleepy', said Nadja Reissland from the university’s Department of Psychology.
"Instead, frequency of yawning in the womb might be related to activity-dependent brain maturation early in gestation."
The study looked at eight female and seven male fetuses from 24 to 36 weeks gestation.
Researchers found that during this period, it was possible to distinguish between yawns and simple mouth openings on ultrasound images based on the4 duration of mouth opening. More than half of all mouth openings were yawns after 24 weeks.
The 4D scans of 15 healthy uteruses showed the frequency of yawning began to decline after 28 weeks.
The study suggests that trends in yawning behaviour could be used to track healthy fetal development.
"The results of this study demonstrate that yawning can be observed in healthy fetuses and extends previous work on fetal yawning. Our longitudinal study shows that yawning declines with increasing fetal age. "
"Given that the frequency of yawning in our sample of healthy fetuses declined from 28 weeks to 36 weeks gestation, it seems to suggest that yawning and simple mouth opening have this maturational function early in gestation."
The study was published in the November Plos One journal.