Biomechanical complications of childbirth, such as obstructed labor, are a major cause of maternal and newborn morbidity and mortality. The impact of birthing position and mobility on pelvic alignment during labor has not been adequately explored. Our objective was to use a previously developed computational model of the female pelvis to determine the effects of maternal positioning and pregnancy on pelvic alignment. We hypothesized that loading conditions during squatting and increased ligament laxity during pregnancy would expand the pelvis. We simulated dynamic joint moments experienced during a squat movement under pregnant and non-pregnant conditions while tracking relevant anatomical landmarks on the innominate bones, sacrum, and coccyx; anteroposterior and transverse diameters, pubic symphysis width and angle, pelvic areas at the inlet, mid-plane, and outlet, were calculated. Pregnant simulation conditions resulted in greater increases in most pelvic measurements - and predominantly at the outlet - than for the non-pregnant simulation. Pelvic outlet diameters in anterior-posterior and transverse directions in the final squat posture increased by 6.1 mm and 11.0 mm, respectively, for the pregnant simulation compared with only 4.1 mm and 2.6 mm for the non-pregnant; these differences were considered to be clinically meaningful. Peak increases in diameter were demonstrated during the dynamic portion of the movement, rather than the final resting position. Outcomes from our computational simulation suggest that maternal joint loading in an upright birthing position, such as squatting, could open the outlet of the birth canal and dynamic activities may generate greater pelvic mobility than the comparable static posture.
Keywords: Ligament laxity; Pelvimetry; Pregnancy; Three-dimensional model; Upright birthing position.
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