During labor and delivery, the baby head tries to find the easiest way to pass the pelvic bone of the mother to reach the vaginal opening. The process is called cardinal movements of labor. And it has 7 major steps. Let’s see them one by one.
First step – Engagement
This is the time when the baby head entered the mother’s pelvis (usually in a transverse position).
If this is your first pregnancy, the baby head might be engaged even before the labor started.
Second step – Decent
This is the time where your baby head moves down into the pelvis. Decent is usually occurred after labor start due to uterine contraction and maternal pushing down effort.
Third step – Flexion
The lowest diameter of the baby head is when the baby flexes its head. it helps the baby to go down through the pelvic bone easily. Flexion usually occurs due to resistance of the pelvic floor. It reduces anteroposterior diameter which makes it easier to pass through the pelvic bone.
Forth step – Internal rotation
As uterine contraction increases and fetal occiput advance through the maternal pelvis, it gets resistance from the maternal pelvic floor. it causes the back of the baby’s head to rotate to anterior from its original transverse position. But the shoulder does not rotate along with the head of the fetus.
Fifth step – Extention
As fetal occiput slip below the pubic arch (which is also called crawling), the fetal head began to extend. And the head of the baby is born.
Sixth step – External rotation
At this point the fetal head and shoulder start to realign. And that is called restitution.
Seventh step – Expulsion
At the same time, the anterior shoulder of the baby passes through the pubic arch, and then the posterior shoulder will pass through the pelvic canal. This is when the whole body of the baby is born.
These 7 mechanisms of labor occur in normal labor which is a normal lie, presentation, and attitude.
See this video to know what cardinal movements of labor really is.
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