Traditionally, the manual palpation of lower back is used to identify the skin insertion point for the epidural needle placement in obstetric patients. Recently, two-dimensional ultrasound (2D US) scanning before the epidural needle insertion proved to improve an accurate determination of inter-vertebral levels and spine midline. 2D US is also useful in determining the depth to the epidural space and needle insertion angle. A three-dimensional ultrasound (3D US) technique is a new advancement in the ultrasound technology. 3D US allows for a real-time, visual guidance of the epidural needle insertion. This study will assess weather 3D US, compared to palpation, can accurately identify the skin needle insertion site for the epidural needle placement.