An ultrasound scan involves transmitting high frequency sound waves through the uterus. These bounce off the baby and the returning echoes are translated by a computer into an image on a screen that reveals the baby’s position and movements. Hard tissues such as bone reflect the biggest echoes and are white in the image and soft tissues appear grey and speckled. Fluids do not reflect any echoes so appear black. It is the contrast between these different shades of white, grey and black that allows your sonographer to interpret the images. Parents look forward to the scan because it gives them the first glimpse of their baby. The sonographer will probably give you a printout of your baby as a keepsake, although some hospitals charge for this. The main purpose of the scan is to check that your baby is growing and developing normally.