The concept of “opening the pelvis” during labor does not involve the bones physically separating but rather maximizing the available space and mobility within the structure to facilitate the baby’s passage. The pelvis is not a single, rigid bone; it is a complex ring of bones connected by joints and ligaments. During pregnancy and labor, hormones cause the ligaments to soften, enabling the joints to shift and widen the pathways for the baby. By understanding and utilizing these inherent movements, a laboring person can actively participate in creating more room for the baby’s descent and rotation.
Understanding Pelvic Mobility During Labor
The bony pelvis presents three distinct areas—the inlet, the mid-pelvis, and the outlet—each requiring specific movements to achieve maximum diameter. The pelvic inlet, the uppermost opening, is best widened when the thighs are rotated externally and spread apart, often accompanied by a backward tilt of the pelvis. This movement encourages the baby’s head to enter the pelvis. As the baby descends through the mid-pelvis, which is the narrowest and most complex part, movement is necessary to help the baby navigate its turns and rotations.
The sacrum, a triangular bone at the base of the spine, plays a direct role in these dimensional changes through two primary motions: nutation and counter-nutation. Nutation, where the sacrum tips forward, increases the space in the pelvic outlet, while counter-nutation, where it tips backward, expands the pelvic inlet. The softening of surrounding muscles and ligaments dictates the range of motion available for these shifts. Actively changing positions throughout labor is the most effective way to utilize these biomechanical principles and encourage continuous progress.
Asymmetrical Movements to Encourage Descent
As the baby moves through the mid-pelvis, asymmetry becomes a powerful tool to encourage rotation. This part of the journey often benefits from uneven weight distribution, which temporarily changes the shape of the pelvic ring to create more side-to-side room. Lunges, whether performed standing with one foot elevated or kneeling with one knee down, lengthen the soft tissues on one side, momentarily widening the opposing side of the pelvis. Walking up stairs or curbs sideways, known as curb walking, is another application of this principle, as the uneven step forces one hip into a higher position than the other.
The side-lying release, a sustained stretch held between contractions, uses a deep, asymmetrical position to relax the pelvic floor and surrounding ligaments. By intentionally creating an imbalance, these movements help the baby “shimmy” past the bony landmarks of the mid-pelvis, especially if labor has slowed or the baby is positioned awkwardly. The goal is to alternate sides to ensure the pelvis is opened evenly for the baby’s rotation and descent.
Optimal Positions to Maximize the Pelvic Outlet
When the baby is low in the pelvis and the pushing stage begins, the focus shifts to maximizing the pelvic outlet. Positions that encourage the tailbone (coccyx) to move backward and the sitting bones to separate are most effective for this stage. Deep squatting, when supported by a partner or a squatting bar, is a highly effective position that can increase the diameter of the pelvic outlet by up to 10 to 15 percent.
The hands-and-knees position allows the sacrum and coccyx to move freely outward, which creates more space posteriorly in the outlet. Supported standing or kneeling, where the upper body is upright, uses gravity to assist with the baby’s descent while still allowing for optimal pelvic alignment. Conversely, pushing while lying flat on the back is generally discouraged because it pushes the tailbone forward, effectively narrowing the pelvic outlet. Side-lying positions, especially when one leg is held up and inward, can also maximize the outlet by utilizing internal hip rotation, which separates the lower pelvic bones.
Supportive Tools and Techniques for Pelvic Opening
Supportive tools and comfort measures can significantly enhance the effectiveness of positional changes. The peanut ball, an oblong, peanut-shaped inflatable device, is particularly valuable for people who have received an epidural and have limited mobility. Placing the peanut ball between the legs while side-lying helps to maintain an open and asymmetrical hip position.
A birthing ball allows for gentle rocking, circular movements, or pelvic tilting while sitting upright, which promotes continuous pelvic mobility and comfort. External techniques, such as the use of a Rebozo, a traditional Mexican shawl, can also be applied. A support person can use the Rebozo to perform a gentle rhythmic sifting or jiggling motion over the hips, which helps to relax the ligaments and encourage the baby’s rotation into a better position.