Biomechanical comparison of squatting and "optimal" supine birth positions.

In obstetric science, it is unknown whether the inherent biomechanical features of the squatting position can be achieved and/or transposed to the supine birth position. In this study Biomechanical features of the squatting position were compared with 2 hyperflexed supine positions for giving birth. Thirteen pregnant women past the 32 weeks of gestational age not in labor were assessed first in the squatting position with the feet flat on the floor, then in the hyperflexed supine position, and finally in the optimal supine position "crushing" the hand of the caregiver onto the bed. For each position, the flexion of the spine associated with the plane of the external conjugate (ANGce) and the pelvis, hip flexion, and abduction were quantified using an optoelectronic motion capture system. A non-invasive strain-gauge-based measuring system was used to track the lumbar curve. An optimal position was defined with a flat lumbar spine and a pelvic inlet plane perpendicular to the lumbar spine (ANGce = 0° ± 5°). For the 13 participants, hip flexion, hip abduction, and the lumbar curve did not differ significantly for the three positions (squatting position, hyperflexed supine position, and OS) in the post-hoc analyses. The optimal supine position induced an ANGce closer to the perpendicular plane than the squatting position (p = 0.002). In the squatting position or in hyperflexed supine position positions, none of the subjects fulfilled the two conditions considered necessary to reach the optimal position. The squatting position was not significantly different from the supine hyperflexed supine position with or without voluntary lordosis correction.