Mechanism of Labor

There are eight classical steps in the normal mechanism of labor as following here:

Engagement

• This is also called lightening or dropping
• The fetus nestles into the pelvis

Descent

• This process starts from the time of engagement until birth and is assessed by the station.
• The fetal head undergoes as it begins its journey through the pelvis.

Flexion

• The fetal head’s nodding forward toward the fetal chest
• While descending through the pelvis, the fetal head flexes so that the fetal chin is touching the fetal chest. This functionally creates a smaller structure to pass through the maternal pelvis

Internal Rotation

• With further descent, the occiput rotates anteriorly and the fetal head assumes an oblique orientation. In some cases, the head may rotate completely to the occiput anterior position.

Extension

• It begins after the head crowns
• This means that the fetal chin is no longer touching the fetal chest.
• It enables the head to emerge when the fetus is in a cephalic position
• The extension of labor is completed when the head passes under the symphysis pubis and occiput and the anterior fontanel, brow, face and chin pass over the sacrum and coccyx and are over the perineum

Restitution

• After the head emerges, the fetal head becomes in a realignment

External Rotation

• The shoulder of fetus externally rotates after head emerging and restitution
  
• The shoulder is in the anteroposterior diameter of the pelvis.

Expulsion

• This is the birth of entire body.