The top of the pelvis is known as the inlet or pelvic brim. It is the first structure of the pelvis that baby needs to engage, or enter, to begin their descent and rotation through the pelvis. Each level of the pelvis opens with certain biomechanical movement patterns, and these movement patterns tend to be the intuitive movements of laboring women who are unmedicated.
We are trying to open the inlet to facilitate engagement during pregnancy and labor! We want baby to enter the pelvis through the inlet, and we can create more space to allow for that.
Opening the Inlet: The Top of the Pelvis
The inlet of the pelvis tends to be wider side to side and narrower front to back. The sacral promontory (where the lumbar spine and sacrum meet) curves inwards into this pelvic level, decreasing the space from the back. Luckily, there is great displacement capability of each pelvic level during pregnancy and labor thanks to the hormone relaxin! The pubic symphysis and SI joints have a greater movement capability than any other time, and allow for a lot of space to be created with movement.
The inlet of the pelvis can be opened with external rotation of the femurs, or wide knees, and a posterior pelvic tilt, or tucking the butt underneath. These tend to be the intuitive movement patterns I observe in laboring women whose babies have not yet engaged into the pelvis. They tend to move more forward and backwards in their rocking; they tend to tuck their butt, either both or just one sided; and they tend to spread their knees apart as they move through each contraction. These would all be observational cues that baby has not yet engaged.
So, what movements would be really helpful to open the inlet and help baby engage?
Movements that incorporate the two elements of wide knees & butt tucked, will open the inlet more! Here are a few examples.
Partner Supported Birth Ball Rocks
Deep, Supported Squat
Movements to open the top of the pelvis involve wide knees and tucking the butt underneath! We can achieve that with intuitive movement, or more directed movements that focus on those movement patterns.
We break down pelvic biomechanics for labor in more depth in our childbirth education courses. There are several lectures on how to open each level of the pelvis with more examples of laboring positions. Our courses are completely self-paced with pre-recorded videos, and you gain access to our private Facebook group where you can ask questions and share your stories to connect with others!