Mechanism of Labour Flashcards
What are the 8 steps in the mechanism of labour?
- Engagement
- Descent
- Flexion of the foetal neck
- Internal Rotation
- Crowning
- Extension of the foetal neck
- External rotation and restitution
- Delivery of the shoulders and body
Describe engagement
Where the largest part of the foetal head fits into the largest diameter of the maternal pelvis
Describe descent
This is where the foetal head descends through the pelvic inlet towards the pelvic floor
What 3 mechanisms cause descent?
- Uterine contractions
- Amniotic Fluid Pressure
- Abdominal muscle contractions
Describe flexion of the foetal neck
The foetal head comes into contact with the pelvic floor during descent, this causes the flexion of the foetal neck (chin to chest).
After flexion, how would we describe the presenting part of the foetus?
sub-occiptio bregmatic
What 2 positions can the foetal head be in during engagement?
- Left occipito transverse (LOT)
2. Right occiptio transverse (ROT)
Describe internal rotation
The pelvic floors gutter shaping (forward, downward slope) allows the foetal head to internally rotate to be in an occipito anterior position, allowing it to lie under the suprapubic arch.
Describe crowning
This is where the widest part of the foetal head successfully negotiates through the narrowest part of the maternal bony pelvis.
How would we clinically define crowning?
Where the foetal head no longer retreats between contractions and is visible at the vulva.
Describe extension
This is where the occiput slips under the suprapubic arch and causes neck extension, the nape of the neck becomes a pivotal point at the arch. This stage also causes stretching of the perineum.
Describe external rotation
This is where the head externally rotates so the baby’s face points towards either the left or right medial thigh of the mother.
Describe restitution
This is where the foetal shoulders change from a transverse position to a anterior-posterior position.
How are the foetal shoulders and body delivered?
The delivering practitioner needs to place downward traction on the foetal head to assist the delivery of the anterior shoulder. This is followed by upward traction of the foetal head to assist delivery of the posterior shoulder. The body will then follow.
