Oxford Women's Health
Ultrasound imaging, also called ultrasound scanning, is a method of obtaining pictures from inside the human body through the use of high frequency sound waves.
Obstetric ultrasound refers to the specialised use of this technique to produce a picture of your unborn baby while it is inside your uterus (womb). The sound waves are emitted from a hand-held nozzle, which is placed on your stomach, and reflection of these sound waves is displayed as a picture of the moving foetus (unborn baby) on a monitor screen. No x-rays are involved in ultrasound imaging.
Measurements of the image of the foetus help in the assessment of its size and growth as well as confirming the due date of delivery.