3D ultrasound is a medical ultrasound technique, often used in obstetric sonography, providing three dimensional images of the fetus.
There are several different scanning modes in medical and obstetric ultrasound. The standard common obstetric diagnostic mode is 2D scanning. In 3D fetal scanning, however, instead of the sound waves being sent straight down and reflected back, they are sent at different angles. The returning echoes are processed by a sophisticated computer program resulting in a reconstructed three dimensional volume image of fetus's surface or internal organs.