A scanner probe is placed on your skin and very high frequency sound waves that are inaudible to the human ear are passed into your body. As the sound waves pass over objects in fluid, they produce a pattern of echoes . These echoes are converted into electrical signals, which are processed and displayed on a screen as a two-dimensional image.
As the scanner probe is guided over your abdomen, you will feel only the cold plastic. If the pregnancy is at a very early stage, you may need to have a full bladder for the scan to be effective; this may cause slight discomfort. You shouldn't feel forced into having a scan. Scans have been...