Lumbar epidural space was narrower in parturients than that in nonpregnant women by ultrasound assessment.

Labor epidural is commonly used to provide both regional anesthesia and postoperative pain relief. Epidural space is supposed to be narrower and deeper in a parturient than that in a nonpregnant woman. The aim of this study was to explore the difference of epidural spaces between parturient and nonpregnant women by ultrasound assessment. Thirty nonpregnant female volunteers and 30 parturients undergoing labor epidurals were enrolled to receive ultrasound examination. A low-frequency (2-5 MHz) curved-array ultrasound probe was used to obtain spinal sonoanatomy for each subject. The longitudinal paramedian scanning plane was used to obtain optimal ultrasound image for spinal sonoanatomy. Primary outcome was evaluated by the diameter and depth of epidural space at three lumbar interspaces (from L2 to L5). The quality of ultrasound images was also compared between the groups by a numerical scoring system (from 0 to 3). The mean diameters of lumbar epidural spaces were 3.03 ± 0.45 mm and 4.44 ± 0.49 mm (p<0.05) for parturients and nonpregnant women, respectively. The mean depths of lumbar epidural spaces for parturients and nonpregnant women were 3.53 ± 0.62 cm and 3.25 ± 0.63 cm, respectively (p<0.05). The mean scores for epidural space image quality were 2.58 ± 0.58 and 2.63 ± 0.53 for parturients and nonpregnant women, respectively (p=0.08). Epidural space is narrower and deeper at lumbar interspaces in obstetrics by ultrasound examination. The quality of ultrasound images did not differ significantly between the groups. These quantitative results improve the understanding of the differences between two groups that have been previously known qualitatively and may help in avoiding complications.