Intrapartum: Key Stages of Labour Flashcards
What 9 key stages can labour be broken down into?
1) Descent
2) Engagement
3) Neck flexion
4) Internal rotation
5) Crowning
6) Extension of the presenting part
7) Restitution
8) External rotation
9) Lateral flexion
What is the most low risk presentation?
Cephalic (vertex) presentation with a longitudinal lie
What are the posterior, lateral & anterior borders of the pelvic inlet?
Posterior: sacral promontory
Lateral: Iliopectineal line
Anterior: pubic symphysis
What are the posterior, lateral & anterior borders of the pelvic oulet?
Posterior: tip of coccyx
Lateral: ischial tuberosity
Anterior: pubic arch
Descent of fetal head position in the pelvic inlet?
The transverse diameter is greater than the antero-posterior (AP) diameter in the pelvic inlet, so the widest circumference of the fetal head descends in a TRANSVERSE position.
I.e. the transverse diameter of the pelvic inlet is bigger than the AP diameter.
Descent of fetal head position in the pelvic outlet?
When it gets closer to the pelvic outlet, the nature of the pelvic floor muscles encourages the fetal head to rotate from a transverse position to an anterior-posterior position, as the AP diameter is greater than the transverse diameter.
I.e. the AP diameter of the pelvic outlet > pelvic inlet.
What is ‘descent’?
The fetus descends into the pelvis.
Note - descent and engagement occur together, rather than as completely separate/distinct stages, so consider them as 2 parts of the same process/stage.
In the primigravida, when is descent likely to occur?
From 38 weeks gestation onwars
In a multigravida, when is descent likely to occur?
May not occur until labour is established.
What is descent encouraged by?
- Increased abdominal tone
- Braxton hicks in the late stages of pregnancy
- Fundal dominance of the uterine contractions
- Increased frequency and strength of contractions during labour
As the head descends, it moves towards the pelvic brim in either the left or right occipito-transverse position.
What does this position mean?
This means the occiput can be facing the left side or right side of the mother’s pelvis.
This allows the widest part of the fetal head to fit through the widest part of the pelvic inlet.
What is enagement?
This is when the largest diameter of the fetal head descends into the maternal pelvis.
The term engagement is referring to the widest part of the fetal head successfully negotiating its way down deep into the maternal pelvis.
How is engagement identified?
Engagement is identified by abdominal palpation, where the fetal head is 3/5th palpable or less.
What does descent occur due to?
1) Uterine contractions
2) Amniotic fluid pressure
3) Abdominal muscle contractions
What occurs during ‘flexion’?
As the fetal head comes into contact with the pelvic floor, cervical flexion occurs (i.e. chin to chest).
This allows the the circumference of the fetal head to reduce to sub-occipitobregmatic (9.5cm).
In this position, the fetal skull has a smaller diameter which assists passage through the pelvis.
What occurs during ‘internal rotation’?
Fetal head rotates from the left or right occipito-transverse position a total of 90-degrees, to an occipital-anterior (occiput facing forward) position, to lie under the subpubic arch.
With each maternal contraction, the fetal head pushes down on the pelvic floor. Following each contraction, a rebound effect supports a small degree of rotation.
Regular contractions eventually lead to the fetal head completing the 90-degree turn.
Further descent leads to the fetus moving into the vaginal canal and eventually, with each contraction, the vertex becomes increasingly visible at the vulva.
Describe the shape of the pelvic floor
Purpose of this shape?
Gutter shape, with a forward and downward slope.
This allows the head to rotate from a left or right occipito-transverse position to an occipito-posterior position.