 We will enroll 30 non-pregnant female volunteers and 30 parturientsASA I-III underwent epidural blocks. A low frequency ultrasound 2-5 MHz with a curved array transducer is used to obtain spinal sonography for each subject. The paramedian axis was used to obtain optimal ultrasound image for spinal sonography. Outcome was evaluated by the diameter and depth of epidural space at three lumbar interspaces. Paired T-test was carried out to evaluate the statistical significance of epidual diameter and depth. 