How the Baby Rotates Through the Pelvis During Labor
1. Baby needs to slide under the sacral promontory (the junction of the low back and the pelvis), and then align their head with the top of the pelvis to then engage into the pelvis.
During Labor The baby tends to begin the descent through the pelvis in a left occiput anterior position, as it allows the baby to slide underneath the sacral promontory, or the junction of the lumbar spine and the sacrum (Davis et al, 2012). The baby will move into flexion, tucking their chin to their chest to present a smaller portion of their head to descend through the pelvis (Davis et al, 2012). The crown of the head’s skull bones mold easier and will help the baby fit through the dynamic pelvic space. After the baby has flexion, they will descent into the pelvic inlet in left occiput transverse to align the widest portion of their head to the widest portion of the pelvis, and then engage, or enter the pelvic inlet.
2. After baby has engaged, they will begin to rotate through the bony structure of the midpelvis until they reach the bottom of the pubic bone.
Many of us spend the majority of labor helping our baby navigate this portion of the pelvis.
After the baby has moved through the pelvic inlet, they begin their descent through the midpelvis. The baby will do an internal rotation to fit the widest part of their head with the widest part of the midpelvis and descend through the midpelvis in a left occiput anterior position (Davis et al, 2012). Baby will continue their internal rotation as they reach the bottom of the midpelvis and begin to enter the outlet, moving into an occiput anterior position in order to have the widest portion of their head aligned with the pelvic floor and widest portion of the pelvic outlet. At the pelvic inlet, the baby’s shoulders are transverse and able to fit into the pelvic inlet’s widest diameter (Davis et al, 2012).
3. Baby then extends their head under the pubic bone!
As your baby is finishing this rotation during labor under the pubic bone, the top of their head is usually visible. When they begin to extend, their head is usually crowning and being born.
The baby will then move into extension, where their head will extend under the pubic arch and be born (Davis et al, 2012). After the head has been born, the baby will externally rotate back in the direction they came to align the head with the shoulders that now need to fit diagonally through the midpelvis and then anteroposterior to the pelvic outlet and pelvic floor (Davis et al, 2012).
4. Then the shoulders align to each level of the pelvis so that they can navigate through after the head has been born.
The shoulders align to the pelvic inlet, usually side to side, then rotate through the midpelvis. Then the shoulders align vertically to the pelvic outlet to be born. The posterior shoulder will be born first, as the sacrum can move easier than the anterior tissues of the vaginal opening, and then the anterior shoulder will be born with the rest of the baby (Davis et al, 2012).
Understanding the cardinal directions and rotations that baby makes through the pelvis helps to demonstrate the importance of opening each pelvic level in occurrence to fetal station. If the baby can move through the pelvis without restriction by aligning to the widest diameters of the pelvic level, it can reduce the prevalence of fetal malpresentation and labor arrest that may increase labor complications and the likelihood of a cesarean section.
childbirth education courses
Reference:
Davis, E., & Harrison, L. (2012). Heart & hands: A midwife's guide to pregnancy and birth. Berkeley, CA: Ten Speed Press.