ANATOMICAL CONFIGURATION OF THE SPINAL COLUMN IN THE SUPINE POSITION .2. COMPARISON OF PREGNANT AND NONPREGNANT WOMEN

To assess the changes in the curvature of the spinal column in the sup ine position during pregnancy, we studied seven pregnant (32-37 weeks of pregnancy) and seven non-pregnant women using magnetic resonance im aging. T1-weighted sagittal midline magnetic resonance images of the s pinal column were obtained with subjects in the supine position with l eft tilt. There was no significant difference in the maximum angle of decline of the lumbar spinal canal between the pregnant (mean 12.4 (SD 3.3)degrees) and non-pregnant (13.4 (3.9)degrees) groups. The maximum angle of incline of the upper thoracic spinal canal was smaller in th e pregnant (15.8 (2.9)degrees) than in the non-pregnant (22.7 (6.0)deg rees) group. The highest point of the lumbar spinal canal was located at a lower lumbar region in the pregnant (median L4-5 (range L4 to L4- 5)) than in the non-pregnant (L4 (L3-4 to L4)) group. The lowest point of the thoracic spinal canal was located at a higher thoracic region in the pregnant (T6-7 (T6 to T7-8)) than in the nonpregnant (T8 (T6-7 to T9)) group. This study revealed that the apex of lumbar lordosis wa s caudad and thoracic kyphosis was reduced in the supine position in t he later stages of pregnancy. These changes in the curvature of the sp inal column may explain, in part, the enhanced cephalad spread of suba rachnoid hyperbaric anaesthetic solutions in the later stages of pregn ancy.