Yawns can be imaged on 4D ultrasounds throughout the second and third trimester, but does it mean anything? Does it mean baby is sleepy? Actually, researchers suggest yawning in the womb can be an indicator that the central nervous system is maturing. The act of yawning acts as a stimulus needed to help the brain mature and can potentially be a sign of healthy development. So not only is it super adorable, yawning in the womb can actually serve a greater purpose.