The idea of “opening the pelvis” describes creating maximum available space for the baby to navigate the birth canal. This process is helped by the hormone relaxin, produced throughout pregnancy, which softens ligaments and joints, particularly in the pelvis. This flexibility allows the bones to move and expand slightly, adapting the pelvis shape as the baby descends during labor.
Understanding Pelvic Mobility During Childbirth
The pelvis is not a fixed structure but a ring of bones and three main joints that can shift and articulate. It consists of two large hip bones connected at the front by the pubic symphysis and at the back to the sacrum and coccyx (tailbone). The baby must pass through three distinct levels of this bony passage, and the most effective movements change depending on the baby’s current location.
The first level is the pelvic inlet, the top opening where the baby engages. Next is the midpelvis, the narrowest passage where the baby typically rotates. The final level is the pelvic outlet, the lower opening through which the baby exits. Because each level is shaped differently, specific positions are used to maximize space. Movements that open the inlet may narrow the outlet, making it important to match the movement to the baby’s station.
Dynamic Movements for Pelvic Inlet and Midpelvis Expansion
Dynamic movements are helpful during early and active labor when the baby is high in the pelvis, working to enter the inlet and descend through the midpelvis. These movements use gravity and joint shifts to create space and encourage optimal rotation. The goal for the inlet is to encourage external hip rotation and a posterior pelvic tilt, which widens the transverse diameter of the top of the pelvis.
A supported deep squat is effective for the pelvic inlet, especially when paired with a slight posterior pelvic tilt. While holding onto stable support, drop the hips low and allow the knees to track wide. This externally rotates the femurs and widens the inlet.
Pelvic rocking movements, such as those performed on a birth ball or in a hands-and-knees position, are also beneficial. Sit on a birth ball with feet flat and wide, then gently roll the hips in a figure-eight pattern or rock the pelvis forward and backward.
The hands-and-knees position (quadruped) is useful for the midpelvis as the baby rotates. The gentle arching and rounding of the back, known as the cat-cow movement, is a pelvic tilt that mobilizes the sacrum. For the midpelvis, asymmetrical positions are key, such as kneeling with one foot flat on the ground in a lunge while the other knee remains on the floor. This uneven stance shifts the pelvic bones on one side, increasing the diameter of the midpelvis to allow for fetal rotation and descent.
Optimal Positions for Pelvic Outlet Widening
As labor progresses into the pushing stage, the focus shifts to widening the pelvic outlet for the baby’s final exit. The outlet opens most effectively with hip flexion and internal rotation of the femurs, which increases the distance between the ischial tuberosities. This is the opposite movement pattern used for the inlet, highlighting the need to change positions as the baby descends.
The side-lying position with a peanut ball placed between the knees or ankles is highly effective. Lying on one side, the top leg is draped over the ball, separating the hips and internally rotating the femur. This position is useful for rest or for pushing when an epidural is in place, as it mechanically increases the outlet’s diameter.
For unmedicated labor, a supported squat remains valuable, but the intention changes. Instead of wide knees, the focus is on tipping the tailbone out (anterior pelvic tilt) to move the sacrum backward. This movement helps increase the front-to-back diameter of the pelvic outlet.
Another asymmetrical position involves a side lunge, where one foot is elevated onto a stable surface. The body shifts toward that leg during a contraction. This variation creates a temporary diagonal expansion in the pelvis to help the baby navigate the final curve of the birth canal.