Mechanism of normal labour Flashcards
List the key steps in the mechanism of labour
Descent Engagement Neck flexion Internal rotation Crowning Extension of the presenting part Restitution External rotation rotation Lateral flexion
Name the most common presentation and lie of the foetus
Cephalic with longitudinal lie
What does normal labour involve?
The widest diameter of the foetus successfully negotiating the widest diameter of the maternal body pelvis
Name the borders of the pelvic inlet
Anterior - pubic symphysis
Lateral - iliopectineal line
Posterior - sacral promontory
Name the borders of the pelvic outlet
Anterior - Pubic arch
Lateral - ischial tuberosity
Posterior - tip of the coccyx
What is the transverse diamter of the pelvic inlet?
13cm
What is the transverse diameter of the mid pelvis?
12cm
What is the transverse diameter of the pelvic outlet?
11cm
What is the antero-posterior diameter of the pelvic inlet
11cm
What is the antero-posterior diameter of the mid pelvis
12cm
What is the antero-posterior diameter of the pelvic outlet?
13cm
Describe the size of the transverse diameter compared to the antero-posterior diameter at the pelvic inlet
Transverse > AP at pelvic inlet
Describe the size of the transverse diameter compared to the antero-posterior diameter at the pelvic outlet
AP > transverse at pelvic outlet
What position is the babys’ head at the pelvic inlet?
Transverse
What position is the babys’ head at the pelvic outlet?
Antero-posterior
What does the fetal head diameter vary with?
Degree of neck flexion
What is the diameter when the head is suboccipitobregmatic (vertex, flexed)
9.5cm
What is the diameter of the head when it is occipitofrontal (vertex, neutral flexion) ?
11cm
What is the diameter of the head when it is submentobregmatic (face)?
9.5cm
What is the diameter of the head when it is verticomental (brow)?
13.5 cm
What is descent?
When the foetus descends into the pelvis
When is descent likely to occur in a primigravida?
38 weeks and onwards
When is descent likely to occur in a multigravida woman?
When labour is established
What is descent encouraged by?
Increase in abdominal muscle tone - maternal effort
Braxton hicks in late stages of pregnancy
Fundal dominance of the uterine contractions in labour
Increased frequency and strength of contractions in labour
Amniotic fluid pressure
What are Braxton hicks?
False labour pains when the uterus contracts and relaxes - 2nd/3rd trimester
Describe what happens to the foetal head as it descends towards the pelvic brim
Moves into either left or right occipito-transverse - occiput facing either left or right side of mother’s pelvis
What is engagement?
When the largest diameter of the foetal head successfully descends deep into the maternal pelvis
What is engagement identified by?
<3/5ths the foetal head palpable
Describe how cervical flexion occurs
A foetus descends through the pelvis, fundal dominance of uterine contraction exerts pressure down the foetal spine towards the occiput, forcing the occiput to come into contact with the pelvic floor
When does cervical flexion occur?
When the foetal head comes into contact with the pelvic floor
How is the presenting part described after neck flexion?
Sub-occipitobregmatic