Well, it's nice and warm in the womb, so you'd forgive the baby if it yawns. Using 4D ultrasound, scientists have captured the fetal yawn and suggested that it may be related to brain development:
Reissland and others used 4D ultrasound scans to capture a rapid sequence of images for eight female and seven male foetuses at 24, 28, 32 and 36 weeks of gestation. All the unborn babies were healthy and were scanned for 20 minutes. The researchers went through the images frame by frame and counted the yawns and other movements made by the babies. Over 58 scans, the team recorded 56 yawns and 27 other mouth movements. Yawns can be distinguished from other movements because a yawning mouth opens more slowly than it closes.
When the scientists analysed the images they found similar yawning rates in boys and girls. But, more surprisingly, yawning decreased steadily from nearly twice every 10 minutes in foetuses at 24 weeks gestation, to none at 36 weeks. The research appears in the journal Plos One.
"Unlike us, foetuses 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," Reissland said.
"Given that the frequency of yawning in our sample of healthy foetuses 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."