Mechanism of Vaginal Delivery

We can be asked by the examiner to demonstrate the mechanism of vaginal birth in the OSCE station for O&G. While explaining the mechanism, we would also have to use the exhibits (mannequin - baby's head, and pelvic bone). Here's the steps in the mechanism:

1. Engagement (definition)
2. Descent and flexion of fetal head
3. Internal rotation - fetal head rotate and assume occipito-anterior position, facing towards maternal rectum.
   
4. Delivery by extension - fetal head extended.
5. Restitution - Fetal head turns 45 degrees to the maternal right hand side, restoring normal relationship with the shoulder.
6. External rotation of the shoulder.

Then, we would assist the delivery by gently pulling the fetal head downward in order to deliver the anterior shoulder before we pull it upward to allow the passage of the posterior shoulder.