The mobility of the pelvis is a powerful tool in childbirth, allowing the laboring person to intentionally create more space for the baby’s descent. The pelvis is composed of multiple bones connected by ligaments that soften and become more flexible during pregnancy due to hormones like relaxin. Strategic changes in body position throughout labor can increase the inner dimensions of the pelvis, giving the baby the mechanical advantage needed to navigate the birth canal. Understanding how movement affects the pelvic openings allows laboring individuals to actively promote progress and potentially reduce labor time.
Maximizing Space for the Pelvic Inlet
The pelvic inlet is the top opening of the pelvis where the baby’s head first engages. This stage is addressed in early labor when the baby is still high. To widen the inlet, the hips need external rotation and abduction, moving the knees away from the body’s midline.
Positions that encourage a wider pelvic inlet involve deep hip flexion and external rotation. A deep, supported squat with the knees spread wide is effective because it increases both the front-to-back and side-to-side dimensions of the inlet. Sitting on a birth ball with wide knees and rocking the pelvis also helps encourage the necessary movements of the pelvic bones.
Asymmetrical positions are helpful for encouraging the baby to move past a tight spot or if the baby is positioned slightly off-center. A kneeling lunge, where one foot is flat on the floor and the other knee is down, creates a different angle on each side of the pelvis. Standing with one foot elevated on a stool or stair also creates an asymmetrical opening, which is crucial for encouraging the baby to rotate and drop lower.
Creating Room for the Pelvic Outlet
The pelvic outlet is the final passage for the baby, and widening this space is most significant during the pushing phase. Maximizing the outlet requires internal rotation of the femurs and allowing the sacrum to move freely. Lying on the back (supine position) restricts the sacrum’s movement and reduces the size of the outlet.
Positions that open the pelvic outlet involve the knees being closer together than the ankles, causing internal rotation of the femur. This rotation moves the ischial tuberosities (“sit bones”) farther apart, widening the side-to-side measurement of the outlet. The hands-and-knees position is effective, especially when the knees are slightly closer together than the feet, allowing gravity to pull the sacrum forward.
Side-lying is a beneficial position, especially with an epidural, as it keeps weight off the sacrum. The top leg is typically brought up and supported. For the outlet, the knees are kept closer together than the ankles to achieve internal rotation. A semi-sitting position with the knees pulled back and wide can also be effective, provided the sacrum is not pressed flat against the bed, which hinders its natural backward movement.
Dynamic Movement and Specialized Tools
Continuous, rhythmic movement complements fixed positions by preventing the pelvis from stiffening and encouraging the baby to navigate the birth canal curves. Slow rocking, swaying, and pelvic tilts while standing or kneeling provide non-strenuous mobility. This dynamic motion helps the baby mold its head and body to the changing shape of the pelvis, easing descent.
Specialized tools like the birth ball and the peanut ball support these movements and positions. Sitting on a birth ball allows for gentle hip circles and figure-eight movements, which relax the pelvic floor muscles and encourage dilation. Leaning over a birth ball while kneeling provides excellent upper body support and maintains a forward-leaning posture favorable for fetal positioning.
The peanut ball is useful for individuals with limited mobility, such as those with an epidural. When placed between the legs while side-lying, it mimics the asymmetrical opening of the pelvis, helping labor progress. By adjusting the placement—between the knees for inlet opening or between the ankles for outlet opening—it can strategically widen different sections of the pelvis while the laboring person rests.
The Active Role of Labor Support
Labor support people facilitate pelvic opening techniques by providing the necessary strength and stability. They assist by physically helping maintain challenging positions, such as supporting a deep squat or holding a propped leg in an asymmetrical lunge. This support allows the laboring person to focus on the contraction while the support person manages the physical demands of the position.
Counter-pressure is a technique applied to the lower back to encourage sacrum movement and relieve pain, especially during “back labor.” In early labor, pressure on the lower sacrum helps open the pelvic inlet by pushing the outlet closed, encouraging the inlet to widen. As labor progresses, the support person can shift to providing a double hip squeeze or “Cook’s counter-pressure,” applying inward pressure to the hips or sitz bones to help the pelvic outlet widen.
The support person also ensures the environment is conducive to position changes and encourages frequent side alternation. When using an asymmetrical position like a lunge or side-lying peanut ball, the laboring person should switch sides every few contractions to ensure symmetrical pelvic opening. This attention to movement and comfort allows the laboring person to remain active and engaged.