Development of fetal yawn compared with non-yawn mouth openings from 24-36 weeks gestation

Abstract

Background: Although some research suggests that fetuses yawn, others disagree arguing that is it simple mouth opening. Furthermore there is no developmental account of fetal yawning compared with simple mouth opening. The aim of the present study was to establish in a repeated measures design the development of fetal yawning compared with simple mouth opening.

Methodology/findings: Video recordings were made of the fetal face and upper torso visualized by means of 4D full frontal or facial profile ultrasound recordings. Fifteen healthy fetuses were scanned four times at 24, 28, 32 and 36 weeks gestation. Yawning was distinguished from non-yawning in terms of the length of time it took to reach the apex of the mouth stretch, with yawns being defined as more than 50% of the total time observed. To assess changes in frequency, a Poisson mixed effects model was fitted to the count of number of yawn and simple mouth opening events with age and gender as fixed effects, and person as a random effect. For both yawns and simple mouth openings a smooth varying age effect was significant. The number of yawns observed declined with age from 28 weeks gestation, whereas simple mouth openings were less frequent and the decline was observed from 24 weeks. Gender was not significant either for yawn and simple mouth openings.

Conclusions/significance: Yawning can be reliably distinguished from other forms of mouth opening with the potential of using yawning as an index of fetal healthy development.

Figure 1. Apex of yawning and non-yawn mouth openings.

The Figure demonstrates that yawning and non-yawn mouth opening cannot be distinguished from a static image at the apex of the event.

Figure 2. Yawning and non-yawn mouth opening sequences from mouth closed to apex and apex to mouth closed.

Figure 3. Observed and fitted yawning and non-yawn mouth opening frequencies by gestational age.

Left panel: Mean observed number of yawn (red solid square) and non-yawn (blue unfilled triangle) mouth openings for each gestational age over 600 seconds of observation. Right panel: Fitted 600-second counts from Poisson mixed effects model for an average fetus for yawning (red solid line) and non-yawn (blue dashed line) mouth openings.