The series of movements that occur on the head in the process of adaptation,
during its journey through the pelvis, is called mechanism of labour.
The principle movements are :-
1. Engagement
2. Discent
3. Flexion
4. Internal rotation
5. Crowning
6. Extension
7. Restitution
8. External rotation of the head and internal rotation of the shoulder
9. Delivery of the shoulder and trunk.
Engagement -
The fetus head enters in brim (inlet) is called engagement. In primigravidae,
engagement occurs before the onset of labour while in multiparae, engagement
occurs in late first stage with the rupture of membranes.
Descent -
Provided there is no undue bony or soft tissue obstruction, descent is a continuous
process. It is slow in first stage but pronounced in second stage. It is completed
with the expulsion of the fetus. Factors facilitating are
- Uterine contraction and retraction.
- Bearing down efforts.
Flexion -
As the head meets the resistance of the birth canal during descent, full flexion is
achieved. Flexion is achieved either due to the resistance offered by the unfolding
cervix, the walls of the pelvis or by the pelvic floor.
Internal rotation -
It is a movement of great importance without which there will be no further descent.
It is probably due to slope of pelvic floor, pelvic shape and inequalities in flexibility
of component parts of the fetus. Torsion of the neck is an inevitable phenomenon
during internal rotation of head. There is no movement of the shoulders from the
oblique diameter as the neck sustains a torsion of only 1/8th of a circle.
Crowning -
After internal rotation of the head , further descent occurs until the subocciput lies
underneath the pubic arch. At this stage, the maximum diameter of the head
(biparietal diameter) stretches the vulval outlet without any recession of the
head even after the contraction is over - called ''crowning of the head''.
Extension -
Delivery of the head takes place by extension through 'couple of force' theory.
The driving force pushes the head in a downward direction while the pelvic floor
offers a resistance in the upward and forward direction. The downward and upward
forces neutralise and remaining forward thrust helping in extension.
Restitution -
It is visible passive movement of the head due to untwisting of the neck sustained
during internal rotation.
External rotation -
It is movement of rotation of the head visible externally due to internal rotation
of the shoulders.
Birth of shoulders and trunk -
After the shoulders are positioned in antero-posterior diameter of the outlet, further
descent takes place until the anterior shoulder escapes below the symphysis pubis
first. By a movement of lateral flexion of the spine, the posterior shoulder sweeps
over the perineum. Rest of the trunk is then expelled out by lateral flexion.
during its journey through the pelvis, is called mechanism of labour.
The principle movements are :-
1. Engagement
2. Discent
3. Flexion
4. Internal rotation
5. Crowning
6. Extension
7. Restitution
8. External rotation of the head and internal rotation of the shoulder
9. Delivery of the shoulder and trunk.
Engagement -
The fetus head enters in brim (inlet) is called engagement. In primigravidae,
engagement occurs before the onset of labour while in multiparae, engagement
occurs in late first stage with the rupture of membranes.
Descent -
Provided there is no undue bony or soft tissue obstruction, descent is a continuous
process. It is slow in first stage but pronounced in second stage. It is completed
with the expulsion of the fetus. Factors facilitating are
- Uterine contraction and retraction.
- Bearing down efforts.
Flexion -
As the head meets the resistance of the birth canal during descent, full flexion is
achieved. Flexion is achieved either due to the resistance offered by the unfolding
cervix, the walls of the pelvis or by the pelvic floor.
Internal rotation -
It is a movement of great importance without which there will be no further descent.
It is probably due to slope of pelvic floor, pelvic shape and inequalities in flexibility
of component parts of the fetus. Torsion of the neck is an inevitable phenomenon
during internal rotation of head. There is no movement of the shoulders from the
oblique diameter as the neck sustains a torsion of only 1/8th of a circle.
Crowning -
After internal rotation of the head , further descent occurs until the subocciput lies
underneath the pubic arch. At this stage, the maximum diameter of the head
(biparietal diameter) stretches the vulval outlet without any recession of the
head even after the contraction is over - called ''crowning of the head''.
Extension -
Delivery of the head takes place by extension through 'couple of force' theory.
The driving force pushes the head in a downward direction while the pelvic floor
offers a resistance in the upward and forward direction. The downward and upward
forces neutralise and remaining forward thrust helping in extension.
Restitution -
It is visible passive movement of the head due to untwisting of the neck sustained
during internal rotation.
External rotation -
It is movement of rotation of the head visible externally due to internal rotation
of the shoulders.
Birth of shoulders and trunk -
After the shoulders are positioned in antero-posterior diameter of the outlet, further
descent takes place until the anterior shoulder escapes below the symphysis pubis
first. By a movement of lateral flexion of the spine, the posterior shoulder sweeps
over the perineum. Rest of the trunk is then expelled out by lateral flexion.
Tq so much
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