Does Body Mass Index Influence the Degree of Pelvic Tilt Produced by a Crawford Wedge?

Background: A pelvic tilt of 15° is standard practice when positioning a woman for caesarean section, and is commonly produced by tilting the operating table or placing a wedge under the right hip. This study investigated whether body mass index affects the degree of pelvic tilt produced when a wedge is used.

Methods: Women undergoing category 3 and 4 caesarean sections were stratified into three groups according to their body mass index at antenatal booking: ≤ 25kg/m(2), 25.1-35kg/m(2) and >35kg/m(2). Twenty women were recruited into each group. Lateral tilt at caesarean section was provided with a Crawford wedge under the right hip and the degree of pelvic tilt was measured using a protractor device.

Results: The median [range] pelvic tilt angle for the groups in order of ascending body mass index were 15° [12-22°], 19° [11-29°] and 17° [2-28°]. There was a significant increase in the variability of pelvic tilt with increasing body mass index (P=0.001). The proportion of patients with pelvic tilt <15° was observed to be 20%, 15% and 30% for women of body mass index ≤ 25kg/m(2), 25.1-35kg/m(2) and >35kg/m(2), respectively.

Conclusion: Variability in pelvic tilt increased with body mass index and was greatest with a booking body mass index >35kg/m(2).