The purpose of this study is to compare accuracy of a new three-dimensional ultrasound (3D US) technique with the traditional palpation method for identification of the needle insertion site on patients' skin before epidural needle placement in pregnant women. The investigators hypothesize that the needle puncture site identified by 3D US is located within a 5 mm radius from the puncture site identified by palpation.

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.

Inclusion Criteria:

• ASA I or II
• Greater than or equal to 19 years old
• Term pregnancy (greater than or equal to 38 weeks gestation age)
• Ability to read English in order to understand the consent form

Exclusion Criteria:

• BMI greater than or equal to 40
• Scoliosis
• Previous difficult regional anesthesia/analgesia
• Previous lower back surgery
• Active labour
• Allergy to epidural tape, surgical paper tape, or felt pen

Term pregnant women expecting neuraxial anesthesia or analgesia for cesarean delivery or labour pain control at BC Women's Hospital.