The concept of “opening your pelvis” during late pregnancy and labor refers to creating maximum space within the bony structure for the baby to descend and rotate. This utilizes the natural mobility of the pelvic joints—particularly the sacroiliac joints and the pubic symphysis—by adjusting the pelvic angle. Strategic sitting positions optimize this space, encouraging the baby into an ideal position for birth and contributing to a smoother labor progression. Proper posture and alignment serve as preparatory training for the physical demands of childbirth.
Optimal Seating Mechanics for Pelvic Space
The foundational principle for opening the pelvis while sitting is achieving an anterior pelvic tilt, which tips the pelvic bowl forward. This forward tilt increases the diameter of the pelvic outlet, giving the baby more room to exit. It is achieved by sitting directly on the “sits bones” (ischial tuberosities) and allowing a slight, natural arch in the lower back.
To maintain this beneficial tilt, the spine must be supported from the base. A simple biomechanical rule is to keep the knees positioned lower than the hips. This prevents the pelvis from rolling backward onto the sacrum, a position that constricts the pelvic outlet.
Sitting on the sacrum causes a posterior pelvic tilt, which tucks the tailbone under and narrows the pelvic outlet. An anterior tilt, by contrast, flares the sitz bones and moves the sacrum away from the baby’s path. This alignment encourages the uterus to lean forward, which helps the baby settle into the optimal head-down, anterior position for birth.
Specific Sitting Positions Using Supportive Aids
Utilizing supportive aids makes it easier to maintain the beneficial anterior pelvic tilt and introduce gentle movement, which aids in pelvic mobility. A labor or exercise ball is a highly effective tool for this purpose. Sitting on a properly inflated ball automatically ensures the hips are higher than the knees, promoting the necessary forward pelvic tilt.
While seated on the ball, gentle, rhythmic movements can help encourage the baby’s descent and rotation. Slow, controlled hip circles or figure-eight motions mobilize the pelvic joints, keeping the area relaxed and flexible. Gentle, vertical bouncing or pelvic rocking can also be performed, but ensure the ball is firm enough so the knees remain below the hip line.
When using a standard chair, a wedge cushion or a folded blanket placed under the back half of the buttocks can elevate the hips, replicating the geometry of sitting on a birth ball. This adjustment forces the pelvis to tilt forward, relieving pressure from the lower back and opening the pelvic space. The feet should remain flat on the floor or on a footrest to establish a stable base of support.
Another beneficial position is tailor sitting, sometimes called the butterfly position, performed on the floor with the soles of the feet touching and the knees bent outward. This position stretches the inner thighs and hip flexors, increasing hip flexibility and strengthening the pelvic floor muscles. Sitting up against a wall or resting the sitz bones on a cushion provides additional support and comfort, allowing focus on maintaining a straight back.
Everyday Sitting Habits to Avoid
Certain common sitting habits actively work against the goal of opening the pelvis and should be minimized, especially in the third trimester. Any position that causes a deep recline, such as lounging on a soft couch or semi-reclining in a chair, forces the pelvis into a posterior tilt. This posture tucks the tailbone under, tightening the abdominal muscles and reducing the space available for the baby to move into an optimal position.
Slouching deeply, where the shoulders are rounded and the spine is curved, also promotes this unfavorable posterior pelvic position. This habit contributes to lower back pain and can encourage the baby to settle into a posterior or “sunny-side-up” position, which can lead to longer, more uncomfortable labor. Consciously shifting to sit on the sits bones rather than collapsing onto the sacrum is a simple postural correction.
Crossing the legs or ankles while sitting is another habit to avoid, as it restricts hip movement and limits circulation in the lower extremities. Crossing the legs can also create an imbalance in the joints and ligaments of the pelvis. Instead, aim to keep the feet flat and slightly apart, distributing the body weight evenly across both hips to maintain proper pelvic alignment.