That depends on what you are looking to see. Many mothers like coming in twice, early on, 16-26 weeks, when they can see the baby as a whole, and then again at 25-34 weeks to see a more detailed face. Between 28 and 32 weeks, your baby develops more fat and gets a more defined face. After 36 weeks, it is more difficult to obtain good pictures since baby is running out of room. The quality of images will depend upon baby’s position, size, movement, maternal tissue and amniotic fluid.