An excerpt from The Birth Book by William and Martha Sears:
"Being upright for birth not only gives baby an easier angle for delivery, but it also widens the passage. When you're up and out of bed your pelvic joints, loosened by the hormones of pregnancy, are free to move and accommodate the little passenger with the large head and broad shoulders. While sitting or lying down, these bones aren't as free to move and your pelvic outlet narrows. In addition, vertical birthing allows more natural stretching of the birth canal tissues and is kinder to the perineum, making episiotomy unnecessary and tears less likely (p. 186)."
Five reasons NOT to birth on your back:
- It can hurt mother's back
- It can harm baby by reducing blood flow/oxygen
- Labor slows and becomes less efficient
- Episiotomy or tears are more likely
- You're working against gravity