The use of ultrasound scanning in pregnancy is referred to as Obstetric Ultrasound. Since its introduction in the late 1950s, Obstetric Ultrasound has become a useful diagnostic tool. It is used to ""see"" the fetus in its mother's womb. In some countries, routine pregnancy ultrasound scans are performed to identify potential defects before birth.

Research indicates that pregnancy ultrasound is safe for the unborn child, unlike radiographs, which use ionizing radiation. Real-time scanners form a continuous picture of the moving fetus on a monitor screen. Very high frequency sound waves of between 3.5 to 7.0 megahertz are generally used for this purpose. They are released from a transducer, which is placed in contact with the maternal abdomen, and is moved around to ""look at"" any particular aspect of the uterus.

Recurring ultrasound beams scan the fetus and are reflected back onto the same transducer. The information obtained from different reflections is recomposed back into a picture on the display screen. The sex of the baby can generally be determined after 16 weeks, depending upon the sonographic machine and aptitude of the operator. Movements such as fetal heartbeat and malformations in the fetus can be gauged and measurements can be made accurately on the images displayed on the screen. Structural abnormalities in the fetus can be dependably diagnosed by an ultrasound scan, and these can usually be performed before 20 weeks.

A full bladder ultrasound is often necessary for the procedure when abdominal scanning is performed in early pregnancy. It is a relatively hassle-free, painless and safe procedure although there may be some uncomfortable sensations from pressure on the full bladder. The conducting gel is non-staining but may feel somewhat cold and damp. Otherwise, there is no feeling at all from the ultrasound rays.