Like regular ultrasounds, 3D and 4D ultrasounds use sound waves to create an image of your baby in your womb. What's different is that 3D ultrasounds create a static three-dimensional image of your baby, while 4D ultrasounds create a live video effect, like a movie -- you can watch your baby smile or yawn. Studies suggest that 3D and 4D ultrasounds are safe. Plus, the images can help doctors spot a problem with your baby and make it easier for them to explain it to you. Ex- cleft lip (defect in the lip), abnormalities of face, limbs.