Apparently, doctors have been at odds for years over whether or not fetuses were actually yawning in the womb. It has been found that babies do, in fact, open their mouths repeatedly while in the uterus, but this study concluded that babies are actually yawning in there.
The study used high resolution, 3D ultrasound images of several fetuses as they developed from the 6th month of pregnancy through the 9th month of pregnancy. The images captured show distinct yawning actions. The yawning action declined, in the study, after the 28th week of pregnancy. The decline in the regularity of the action has led some researchers to believe that the action is linked to the development of the fetus. Further research is planned.