4D Ultrasound Reveals Fetuses Yawn in the Womb

Unborn infants are known to swallow, hiccup, and stretch in the womb, but new ultrasound research concluded that they also yawn.

The four-dimensional (4D) full frontal or facial profile ultrasound recordings scans of 15 healthy fetuses, by Durham University (Durham, UK) and Lancaster University (Lancaster, UK), also suggest that yawning is a developmental process that could potentially provide clinicians with another index of a fetus’ health. The study was published November 21, 2012, in the journal PLOS ONE.


While some researchers have suggested that fetuses yawn, others have disagreed and claim it is simple mouth opening. However, the new research distinctly differentiated “yawning” from “non-yawn mouth opening” based on the duration of mouth opening. The researchers did this by using the 4D video footage to closely examine all incidents where a mouth stretch occurred in the fetus.

Using their newly developed criteria, the investigators discovered that over 50% of the mouth openings seen in the study were classed as yawns. The study was conducted on seven male and eight female fetuses from 24 to 36 weeks gestation. The researchers discovered that yawning decreased from 28 weeks and that there was no significant difference between boys and girls in yawning frequency.

Although the function and significance of yawning is still unclear, the findings suggest that yawning could be tied to fetal development, and as such could provide an additional medical indication of the health of the unborn infant. Lead researcher, Dr. Nadja Reissland, of Durham University’s department of psychology, said, “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. Unlike us, fetuses do not yawn contagiously, nor do they yawn because they are sleepy. Instead, the frequency of yawning in the womb may be linked to the maturing of the brain early in gestation. 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.”

Moreover, Dr. Reissland added that yawning could be associated with central nervous system maturation, however, additional research involving mother and fetus would be required to study this hypothesis.

Related Links:
Durham University
Lancaster University