Mechanisms of Labour Flashcards
What is meant by the mechanisms of labour?
the changes in position of the foetus as it passes through the maternal pelvis during labour
What mnemonic is used to remember the 7 cardinal movements?
- engagement
- descent
- flexion
- internal rotation & crowing
- extension
- restitution
- external rotation & delivery
In relation to what presentation are the cardinal movements described?
they are described in relation to a cephalic (vertex) presentation with a longitudinal lie
this is the most common and lowest risk position
Why is the degree of neck flexion important during delivery?
- the circumference of the foetal head varies with different degrees of neck flexion
occipitofrontal / verticomental are too large to pass through the pelvis
What is important to remember about descent and engagment?
they occur together
What is meant by foetal descent?
When does it occur?
- the foetus descends through the pelvic inlet towards the pelvic floor
- this occurs from 38 weeks gestation onwards in the primigravida
- it often does not occur until labour is established in a multigravida woman
primigravida = a woman who is pregnant for the first time
What encourages foetal descent?
- increased abdominal muscle tone
- Braxton-Hicks contractions in the late stages of pregnancy
- fundal dominance of uterine contractions
- increased frequency + strength of contractions during labour
What is meant by fundal dominance of contractions?
- contractions are initiated at the fundus of the uterus
- they move in a wave-like manner from this point
How does the head of the foetus move as it descends?
- it moves towards the pelvic brim
- in either the left or right occipito-transverse position
i.e. the occiput can be facing the left or right side of the mother’s pelvis
What is meant by engangement?
- the largest diameter of the foetal head fits into the largest diameter of the pelvis
- the head moves towards the pelvic brim in either the right / left occipitotransverse position
Why does the foetal head need to move into the occipitotransverse position during engagement?
to allow the widest part of the foetal head to fit through the widest part of the pelvic inlet
How can engagement be identified externally?
abdominal palpation
- the foetal head is 3/5th palpable or less
What happens during the flexion stage?
- the foetal occiput comes into contact with the pelvic floor
- when this happens, cervical flexion occurs
- the fetal neck flexes (chin to chest) to allow the circumference of the fetal head to reduce to sub-occipitobregmatic (9.5cm)
the foetal skull has a smaller diameter to pass through the pelvis in this position
What happens during the internal rotation stage?
- the gutter shape of the pelvic floor encourages the head to rotate
- it rotates 90-degrees from the L/R occipitotransverse position to the occipitoanterior position
- the head now lies under the subpubic arch
the occiput faces forwards
What happens during the crowning phase?
the head is “crowning” when the widest diameter of the head has successfully passed through the narrowest part of the pelvis
What happens during the extension phase?
- the occiput slips beneath the suprapubic arch, which allows the head to extend
- the head is now born
- the head faces the maternal back (occiput is anterior)
What happens during restitution?
- the head externally rotates to face the L / R medial thigh of the mother
- this occurs to allow the foetus to naturally align its head with its shoulders
Following restitution, how can delivery be assisted?
downward traction:
- assists delivery of the anterior shoulder below the suprapubic arch
upward traction:
- this follows to assist delivery of the posterior shoulder
the fetal body is delivered by contractions and traction should only assist safe negotiation
