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Station 4
Dr J Herold
Station learning objectives:
1. Understand what is meant by the term ‘mechanisms of labour’
2. be able to describe the passage of the foetus through the birth canal in a skull
presentation
3. understand what is meant by the following terms:
- engagement
- descent & flexion
- internal rotation
- extension
- restitution
- external rotation
4. demonstrate with a clear commentary the mechanisms of labour
The passage (negotiating the ‘S’ bends) of the foetus through the pelvis / birth canal
during the second stage of labour is known as the mechanisms of labour.
1. ENGAGEMENT
The foetus is said to have engaged when the biparietal diameter has passed
through the pelvic inlet, in an occipito-transverse position
Engagement of the presenting part is assessed by:
abdominal examination – 5ths above pelvic brim
Leopold’s 4th manouevre deep pelvic grip
- if your hands converge, presenting part is not engaged
- if your hands diverge, presenting part is engaged
completely
above
sinciput
sinciput
high,
easily felt,
occiput
occiput
easily felt felt
sinciput
felt,
occiput
just felt
sinciput
felt,
occiput
not felt
none
of head
palpable
2. DESCENT
Occurs as a result of the active forces (uterine contractions & bearing down)
throughout labour, and the foetal head descends from the inlet into the cavity
/ mid-pelvis
3. FLEXION
Occurs as a result of the resistance from the lower segment of the uterus and
the levator ani muscles. Foetal head flexes onto chest
4. INTERNAL ROTATION
Lowest presenting part (occiput in normal labour) encounters pelvic floor
resistance and thus rotates to become anterior
5. EXTENSION
Occurs in order for the foetal head
to negotiate the natural curves of
the pelvis therefore as extension
occurs the parts of the foetal head
move over the perineum in the
following order:
vertex, forehead, face & chin
6. RESTITUTION
The head rotates (outside the body)
the opposite of internal rotation in
order to realign with the foetal
shoulders which lie in the AP
diameter behind the symphisis pubis
7. EXPULSION
The anterior shoulder is delivered first from below the symphisis pubis,
followed by the posterior shoulder over the perineum.
Finally the trunk is born by lateral flexion.
Following expulsion the umbilical cord is clamped.