Mechanism of labour

1
Mechanism of labour

• Descent

• Relation to practice

• The fetus begins to
• descend into the pelvis
• due to the force of gravity
• and downward pressure
• of the contractions

• Primip-may occur before the
• onset of labour
• Multip-not until onset of
• labour due to laxity of
• uterine/abdo muscles
• Educate re optimal fetal
• positioning
• Adequate abdominal palpation
• Upright and mobile once in
• Labour, continual support

2
Mechanism of labour

• Flexion

• Relation to practice

• As the fetus descends the chin
• touches the chest (arms begin
• to cross) and the attitude of
• flexion is adopted. This is
• increased further when the
• head meets the resistance of
• the birth canal

• Upright position to assist with
• gravity
• When resting, adopt the left
• lateral position (OFP)
• Observation of the
• contractions-are they regular,
• do they appear to be
• increasing in strength and
• becoming expulsive?

3
Mechanism of labour

• Internal rotation

• Relation to practice

• As the occiput reaches the
• resistance of the pelvic floor, it
• rotates forward 45 degrees.
• The slope of the pelvic floor
• aids this rotation forward and
• allows the head to emerge in
• the longest diameter of the
• pelvis (anterposteior)

• Fully dilated, station of the head
• Vertex may or may not be
• visible
• Upright position-kneeling,
• squatting
• May be spontaneously pushing
• Would you encourage
• mechanical pushing or allow
• for natural descent?

4
Mechanism of labour

• Crowning

• Relation to practice

• The head has crowned when it
• escapes under the pubic arch
• and no longer recedes
• between contractions because
• the widest transverse diameter
• of the head is born
• Extension
• With slight extension the
• bregma, forehead, face and chin
• will pass over the perineum and
• the head is born

• May be
• spontaneously/mechanically
• pushing or still breathing
• through contractions, how
• long can the second stage last?
• Introverted in her behaviour
• and may adopt alternative
• Position, bending towards the
• floor with knees apart

5
Mechanism of labour

• Restitution

• Relation to practice

• When the head is born it will
• turn to the left or the right,
• righting itself with the
• shoulders. The shoulders then
• rotate (similar action to that of
• the head) and lie in the
• anteroposterior diameter of
• the pelvis. Rotation follows
• the same direction as restitution

• No need to do anything, allow
• time for restitution (you may
• see a small part of the anterior
• shoulder). Wait for the next
• contraction to deliver the
• remainder of the body
• (Drs are often too quick in
• trying to deliver the body)

6
Mechanism of labour

• Lateral flexion

• Relation to practice

• In most supine or semi
• recumbent birthing positions
• the anterior shoulder will be
• born first (under the pubic
• arch) and the posterior
• shoulder will pass over the
• perineum

• If the woman is on all fours or
• leaning forward then the
• posterior shoulder may be
• born first due to gravity and
• the effect of the birth canal-
• the curve of carus-this causes
• the trunk of the baby to flex
• sideways as it is born