Ultrasound is a useful technique for looking at the growth of a foetus. Photograph: babyscans.co.uk
Ultrasound uses high-frequency sound waves that are inaudible to the human ear. These waves travel through the body and the echoes create images of the internal structures or of a foetus. Ultrasound are beneficial for imaging organs that are situated deep within body cavities, and as ultrasound doesn't involve ionising radiation, is believed to be completely safe.
Ultrasound works by a transducer (the handheld device that is held against the skin surface) converting an electric current into high-frequency sound waves. The sound waves emitted by the transducer are focused in a narrow beam that passes through the body's soft tissues and fluid, and are then reflected at a point where different densities meet. The transducer also acts as a receiver by converting the reflected echoes into electrical signals, which is processed by a computer as a 2D image.
Most pregnant women will have at least one ultrasound scan during their pregnancy. Ultrasound can also be used to image a newborn baby's brain. Using ultrasound in this way can identify any bleeding into the brain, which can a potential problem in newborns.
Ultrasound is also commonly used to look at internal organs and fluid-filled structures. It is also used to examine the heart's structure and movement.
Ultrasound is not thought to have any risks, and can be repeated as often as necessary. Because of this, it is the only imaging technique believed to be safe for routine foetus screening.