It is very unfortunate that we think a birthing woman should only be on her back to deliver her child.
This is the WORST position a woman can be in as it works against gravity. The effort of pushing is already intense. This makes this potentially overwhelming job much harder, longer and stimulates frustration for mother and care providers. That frustration and longer time frame, which usually causes fear for all involved, can then have the unwanted outcome of a c-section.

Lying down puts pressure and strain on the sacrum which can cause damage, bruising or pain after delivery. Sometime for months on end. This is called symphysis pubic dysfunction. That trauma can complicate future pregnancies with the weight of baby making carrying your baby quite uncomfortable or consistently painful.

In the lithotomy position, pressure added by a woman’s legs being held back firmly and powerfully can result in excruciating postpartum Supra-pubic pain, difficulty walking where crutches or wheelchair use is required. Bladder dysfunction is a complication as well though more rare.

Ideal birth positions make all the difference in the safety of the perineum and pelvic floor. They allow the sacrum and coccyx the freedom to rotate fully and the rest of the pelvis to open while keeping contractions strong and close together.
Ideal birth positions are:

Hands and Knees
Sitting Positions
Side-Lying
Upright or Standing
And my FAVORITE: Squatting

Choose a birthing positions that best supports the quality of your contractions while enhancing your ability to push. Education and support! It’s all you need to create the IDEAL birth for you!