Objective
To investigate a biomechanism of pelvic pain in pregnancy by use of motion analyzer.

Method
Ten pregnant women in the early third trimester and 10 healthy women as control were enrolled. A gait analysis by a Vicon 370 motion analyzer system was performed to investigate the dynamic lumbo-pelvic motion of pregnancy in biomechanical aspects.

Results
The mean maximal surface lordotic angle of pregnant women was 24.42⁑3.98 degrees, the mean minimal surface lordotic angle 20.64⁑4.27 degrees, and the mean maximal surface lordotic angle of controls was 21.61⁑2.43 degrees, the mean minimal surface lordotic angle 18.38⁑2.29 degrees (p＞0.05). The mean maximal anterior pelvic tilt of pregnant women was 21.11⁑5.91 degrees, and the mean maximal anterior pelvic tilt of controls was 15.28⁑4.94 degrees (p＜0.05).

Conclusion
The angle of lumbar lordosis was within normal ranges but the anterior pelvic tilt was increased significantly in pregnancy. This can place mechanical stress on lumbo-pelvic region. This dynamic sagittal imbalance of the spine may be a considerable cause for low back and pelvic pain in pregnancy as indicated by the results of this study.