Ultrasound is used in both obstetrics (pregnancy) and gynaecology, using high frequency sound waves to create an image.
Ultrasound waves are directed into the abdomen by a transducer placed on the skin. The sound waves are reflected by the interface between organs with different densities.
The clarity of the image depends on the fequency of the sound waves and the distance of the transducer from the region being examined. Higher frequencies will allow more detail to be seen but will not travel as far into the body.
The closer the transducer can get, the higher the frequency that can be used and the more detail that can be seen.
Ultrasound can be performed at different stages of pregnancy: