What's the Difference between 2D, 3D, and 4D Ultrasound?

Many of our clients at 3D BabyVision -- 3D Ultrasound ask us what's the difference between 2D, 3D, and 4D ultrasound. 

 The following video provides some insight to the subject:

https://www.youtube.com/watch?v=OBV7i9zRAto